Enhance GitHub Actions with permissions and concurrency

Added read permissions for contents, write permissions for pages,
and write permissions for id-token to the workflow. Introduced
a concurrency group for pages to manage concurrent deployments
without cancellations. These updates optimize security and
improve deployment reliability by controlling job concurrency.

.github/workflows/crystal.yml

@@ -6,6 +6,15 @@ on:
   pull_request:
     branches: [master]
 
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: "pages"
+  cancel-in-progress: false
+
 jobs:
   docs:
     runs-on: ubuntu-latest