Add infrastructure to validate GitHub Actions workflows

A task and GitHub Actions workflow are provided here for validating the project's GitHub Actions workflows.

On every push or pull request that affects the repository's GitHub Actions workflows, and periodically, the workflow
will validate them against the JSON schema.

Author: per1234

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

@@ -0,0 +1,48 @@
+# Source: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/check-workflows-task.md
+name: Check Workflows
+
+env:
+  # See: https://github.com/actions/setup-node/#readme
+  NODE_VERSION: 16.x
+
+# See: https://docs.github.com/actions/using-workflows/events-that-trigger-workflows
+on:
+  push:
+    paths:
+      - ".github/workflows/*.ya?ml"
+      - "package.json"
+      - "package-lock.json"
+      - "Taskfile.ya?ml"
+  pull_request:
+    paths:
+      - ".github/workflows/*.ya?ml"
+      - "package.json"
+      - "package-lock.json"
+      - "Taskfile.ya?ml"
+  schedule:
+    # Run every Tuesday at 8 AM UTC to catch breakage resulting from changes to the JSON schema.
+    - cron: "0 8 * * TUE"
+  workflow_dispatch:
+  repository_dispatch:
+
+jobs:
+  validate:
+    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 workflows
+        run: task --silent ci:validate

README.md

@@ -10,6 +10,7 @@
 [![Check Python status](https://github.com/arduino/compile-sketches/actions/workflows/check-python-task.yml/badge.svg)](https://github.com/arduino/compile-sketches/actions/workflows/check-python-task.yml)
 [![Check Taskfiles status](https://github.com/arduino/compile-sketches/actions/workflows/check-taskfiles.yml/badge.svg)](https://github.com/arduino/compile-sketches/actions/workflows/check-taskfiles.yml)
 [![Check ToC status](https://github.com/arduino/compile-sketches/actions/workflows/check-toc-task.yml/badge.svg)](https://github.com/arduino/compile-sketches/actions/workflows/check-toc-task.yml)
+[![Check Workflows status](https://github.com/arduino/compile-sketches/actions/workflows/check-workflows-task.yml/badge.svg)](https://github.com/arduino/compile-sketches/actions/workflows/check-workflows-task.yml)
 [![Spell Check status](https://github.com/arduino/compile-sketches/actions/workflows/spell-check-task.yml/badge.svg)](https://github.com/arduino/compile-sketches/actions/workflows/spell-check-task.yml)
 [![Sync Labels status](https://github.com/arduino/compile-sketches/actions/workflows/sync-labels-npm.yml/badge.svg)](https://github.com/arduino/compile-sketches/actions/workflows/sync-labels-npm.yml)
 [![Test Python status](https://github.com/arduino/compile-sketches/actions/workflows/test-python-poetry-task.yml/badge.svg)](https://github.com/arduino/compile-sketches/actions/workflows/test-python-poetry-task.yml)

Taskfile.yml

@@ -11,6 +11,7 @@ tasks:
     desc: Check for problems with the project
     deps:
       - task: action:validate
+      - task: ci:validate
       - task: general:check-formatting
       - task: general:check-spelling
       - task: markdown:check-links
@@ -53,6 +54,34 @@ tasks:
             -s "{{.ACTION_METADATA_SCHEMA_PATH}}" \
             -d "action.yml"
 
+  # Source: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/assets/check-workflows-task/Taskfile.yml
+  ci:validate:
+    desc: Validate GitHub Actions workflows against their JSON schema
+    vars:
+      # Source: https://github.com/SchemaStore/schemastore/blob/master/src/schemas/json/github-workflow.json
+      WORKFLOW_SCHEMA_URL: https://json.schemastore.org/github-workflow
+      WORKFLOW_SCHEMA_PATH:
+        sh: task utility:mktemp-file TEMPLATE="workflow-schema-XXXXXXXXXX.json"
+      WORKFLOWS_DATA_PATH: "./.github/workflows/*.{yml,yaml}"
+    deps:
+      - task: npm:install-deps
+    cmds:
+      - |
+        wget \
+          --quiet \
+          --output-document="{{.WORKFLOW_SCHEMA_PATH}}" \
+          {{.WORKFLOW_SCHEMA_URL}}
+      - |
+        npx \
+          --package=ajv-cli \
+          --package=ajv-formats \
+          ajv validate \
+            --all-errors \
+            --strict=false \
+            -c ajv-formats \
+            -s "{{.WORKFLOW_SCHEMA_PATH}}" \
+            -d "{{.WORKFLOWS_DATA_PATH}}"
+
   docs:generate:
     desc: Create all generated documentation content
     # This is an "umbrella" task used to call any documentation generation processes the project has.