Adds GitHub Action workflow file

.github/workflows/check-a11y-of-changed-content.yaml

@@ -0,0 +1,68 @@
+name: Check accessibility of changed content
+
+on:
+  workflow_dispatch:
+  push:
+    branches:
+      - gh-pages
+  pull_request:
+
+permissions:
+  contents: read
+  pull-requests: read
+
+concurrency:
+  group: '${{ github.workflow }} @ ${{ github.event.pull_request.head.label || github.head_ref || github.ref }}'
+  cancel-in-progress: true
+
+jobs:
+  check-a11y-of-changed-content:
+    name: Check accessibility of changed content
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Fetch gh-pages branch
+        run: >-
+          git fetch origin gh-pages
+          && git branch gh-pages origin/gh-pages;
+
+      - name: Calculate URLs and output to JavaScript module
+        run: >-
+          chmod +x ./generate_pa11y_ci_urls_from_git_diff.sh
+          && ./generate_pa11y_ci_urls_from_git_diff.sh gh-pages
+          >> ./pa11y-ci-urls.js;
+
+      - name: Log contents of resulting JavaScript module
+        run: cat ./pa11y-ci-urls.js;
+
+      - name: Setup Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: 2.3
+
+      - name: Install gems
+        run: bundle config path vendor/bundle && bundle install
+
+      - name: Run the blog
+        run: bundle exec jekyll serve &
+
+      - name: Setup Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20.10.x
+          cache: npm
+
+      - name: Install NPM dependencies
+        run: npm ci
+
+      - name: Setup Chrome
+        uses: browser-actions/setup-chrome@v1
+        id: setup-chrome
+
+      - name: Wait for blog to be running
+        run: npx wait-on http://localhost:4000 --timeout 60000
+
+      - name: Run pa11y-ci
+        run: CHROMIUM_BIN=$(which chrome) npx pa11y-ci