Update infrastructure for action metadata validation

A task and GitHub Actions workflow are provided here for validating the action.yml metadata file of GitHub Actions
actions.

On every push or pull request that affects the metadata file, and periodically, validate action.yml against its JSON
schema.

.github/workflows/check-action-metadata-task.yml

@@ -0,0 +1,76 @@
+# Source: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/check-action-metadata-task.md
+name: Check Action Metadata
+
+env:
+  # See: https://github.com/actions/setup-node/#readme
+  NODE_VERSION: 16.x
+
+# See: https://docs.github.com/en/actions/reference/events-that-trigger-workflows
+on:
+  create:
+  push:
+    paths:
+      - ".github/workflows/check-action-metadata-task.ya?ml"
+      - "action.ya?ml"
+      - "package.json"
+      - "package-lock.json"
+      - "Taskfile.ya?ml"
+  pull_request:
+    paths:
+      - ".github/workflows/check-action-metadata-task.ya?ml"
+      - "action.ya?ml"
+      - "package.json"
+      - "package-lock.json"
+      - "Taskfile.ya?ml"
+  schedule:
+    # Run every Tuesday at 8 AM UTC to catch breakage from changes to the JSON schema.
+    - cron: "0 8 * * TUE"
+  workflow_dispatch:
+  repository_dispatch:
+
+jobs:
+  run-determination:
+    runs-on: ubuntu-latest
+    outputs:
+      result: ${{ steps.determination.outputs.result }}
+    steps:
+      - name: Determine if the rest of the workflow should run
+        id: determination
+        run: |
+          RELEASE_BRANCH_REGEX="refs/heads/[0-9]+.[0-9]+.x"
+          # The `create` event trigger doesn't support `branches` filters, so it's necessary to use Bash instead.
+          if [[
+            "${{ github.event_name }}" != "create" ||
+            "${{ github.ref }}" =~ $RELEASE_BRANCH_REGEX
+          ]]; then
+            # Run the other jobs.
+            RESULT="true"
+          else
+            # There is no need to run the other jobs.
+            RESULT="false"
+          fi
+
+          echo "result=$RESULT" >> $GITHUB_OUTPUT
+
+  validate:
+    needs: run-determination
+    if: needs.run-determination.outputs.result == 'true'
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v3
+        with:
+          node-version: ${{ env.NODE_VERSION }}
+
+      - name: Install Task
+        uses: arduino/setup-task@v1
+        with:
+          repo-token: ${{ secrets.GITHUB_TOKEN }}
+          version: 3.x
+
+      - name: Validate action.yml
+        run: task --silent action:validate

.gitignore

@@ -18,3 +18,5 @@ venv/
 *.bak
 *.code-workspace
 *.sublime-workspace
+
+/node_modules/

README.md

@@ -1,5 +1,6 @@
 # `arduino/compile-sketches` action
 
+[![Check Action Metadata status](https://github.com/arduino/compile-sketches/actions/workflows/check-action-metadata-task.yml/badge.svg)](https://github.com/arduino/compile-sketches/actions/workflows/check-action-metadata-task.yml)
 [![Tests](https://github.com/arduino/compile-sketches/workflows/Test%20Python%20code/badge.svg)](https://github.com/arduino/compile-sketches/actions?workflow=Test+Python+code)
 [![Lint](https://github.com/arduino/compile-sketches/workflows/Lint%20Python%20code/badge.svg)](https://github.com/arduino/compile-sketches/actions?workflow=Lint+Python+code)
 [![Spell Check](https://github.com/arduino/compile-sketches/workflows/Spell%20Check/badge.svg)](https://github.com/arduino/compile-sketches/actions?workflow=Spell+Check)

Taskfile.yml

@@ -0,0 +1,72 @@
+# See: https://taskfile.dev/#/usage
+version: "3"
+
+tasks:
+  check:
+    desc: Check for problems with the project
+    deps:
+      - task: action:validate
+
+  # Source: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/assets/check-action-metadata-task/Taskfile.yml
+  action:validate:
+    desc: Validate GitHub Actions metadata against JSON schema
+    vars:
+      ACTION_METADATA_SCHEMA_PATH:
+        sh: task utility:mktemp-file TEMPLATE="github-action-schema-XXXXXXXXXX.json"
+    deps:
+      - task: npm:install-deps
+    cmds:
+      - |
+        wget \
+          --quiet \
+          --output-document="{{.ACTION_METADATA_SCHEMA_PATH}}" \
+          https://json.schemastore.org/github-action
+      - |
+        npx \
+          ajv-cli \
+            validate \
+            --strict=false \
+            -s "{{.ACTION_METADATA_SCHEMA_PATH}}" \
+            -d "action.yml"
+
+  # Source: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/assets/npm-task/Taskfile.yml
+  npm:install-deps:
+    desc: Install dependencies managed by npm
+    run: once
+    cmds:
+      - npm install
+
+  # Make a temporary file named according to the passed TEMPLATE variable and print the path passed to stdout
+  # Source: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/assets/windows-task/Taskfile.yml
+  utility:mktemp-file:
+    vars:
+      RAW_PATH:
+        sh: mktemp --tmpdir "{{.TEMPLATE}}"
+    cmds:
+      - task: utility:normalize-path
+        vars:
+          RAW_PATH: "{{.RAW_PATH}}"
+
+  # Make a temporary folder named according to the passed TEMPLATE variable and print the path passed to stdout
+  # Source: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/assets/windows-task/Taskfile.yml
+  utility:mktemp-folder:
+    vars:
+      RAW_PATH:
+        sh: mktemp --directory --tmpdir "{{.TEMPLATE}}"
+    cmds:
+      - task: utility:normalize-path
+        vars:
+          RAW_PATH: "{{.RAW_PATH}}"
+
+  # Print a normalized version of the path passed via the RAW_PATH variable to stdout
+  # Source: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/assets/windows-task/Taskfile.yml
+  utility:normalize-path:
+    cmds:
+      - |
+        if [[ "{{.OS}}" == "Windows_NT" ]] && which cygpath &>/dev/null; then
+            # Even though the shell handles POSIX format absolute paths as expected, external applications do not.
+            # So paths passed to such applications must first be converted to Windows format.
+            cygpath -w "{{.RAW_PATH}}"
+        else
+          echo "{{.RAW_PATH}}"
+        fi