chore(deps): Configure Dependabot to ignore constructs

Users of `@guardian/cdk` must be on the exact version of the `aws-cdk` and `construct` dependencies,
else they see issues like this in CI (source guardian/cdk-playground#192):

```console
    lib/cdk-playground.ts:17:52 - error TS2345: Argument of type 'this' is not assignable to parameter of type 'IConstruct'.
      Type 'CdkPlayground' is not assignable to type 'IConstruct'.
        Types of property 'node' are incompatible.
          Type 'import("/home/runner/work/cdk-playground/cdk-playground/cdk/node_modules/constructs/lib/construct").Node' is not assignable to type 'import("/home/runner/work/cdk-playground/cdk-playground/cdk/node_modules/@guardian/cdk/node_modules/constructs/lib/construct").Node'.
            Types have separate declarations of a private property 'host'.

    17     AppIdentity.taggedConstruct(CdkPlayground.app, this);
```

The above was caused by merging #1195 w/out creating a new major version release,
and it consequently being included in the 41.0.1 patch.

In this change, we remove management of `constructs` from Dependabot in favour of bumping the version ourselves (and creating a new major release when doing so).

.github/dependabot.yml

@@ -8,6 +8,7 @@ updates:
       interval: 'weekly'
     commit-message:
       prefix: "chore(deps): "
+
   - package-ecosystem: 'npm'
     directory: '/'
     schedule:
@@ -18,9 +19,16 @@ updates:
       prefix: "chore(deps): "
     # force the lockfile and package.json to be updated
     versioning-strategy: increase
-    # We update AWS CDK libraries ourselves (via `script/update-aws-cdk`) as this is a breaking change for users, and it results in a new major version being released
+
+    # Users of `@guardian/cdk` must be on the exact version of these dependencies.
+    # Any update to them in `package.json` should create a new major version of `@guardian/cdk`.
+    # New versions of these dependencies are published quite often. In the case of `constructs`, see https://github.com/aws/constructs/issues/970.
+    # In order to reduce the frequency of new major versions of `@guardian/cdk`, we'll manage these dependencies ourselves via `script/update-aws-cdk`.
     ignore:
+      - dependency-name: "aws-cdk"
       - dependency-name: "aws-cdk-lib"
+      - dependency-name: "constructs"
+
   - package-ecosystem: 'npm'
     directory: '/tools/integration-test'
     schedule:
@@ -34,3 +42,4 @@ updates:
     ignore:
       - dependency-name: "aws-cdk"
       - dependency-name: "aws-cdk-lib"
+      - dependency-name: "constructs"

package.json

@@ -24,7 +24,7 @@
     "release": "semantic-release",
     "release:docs": "rm -rf target && typedoc && gh-pages -d target -u \"github-actions-bot <[email protected]>\"",
     "serve:docs": "rm -rf target && typedoc && serve target",
-    "update-aws-cdk": "ncu \"aws-cdk-lib\" \"aws-cdk\" --upgrade --deep --target minor",
+    "update-aws-cdk": "ncu \"aws-cdk-lib\" \"aws-cdk\" \"constructs\" --upgrade --deep --target minor",
     "cli:dev": "ts-node src/bin/index.ts"
   },
   "devDependencies": {