Add a script to upstream WPT changes via a GitHub Action

This is a modified version of the webhook found at
servo/upstream_wpt_webhook and deployed via SaltStack. It is updated to
use modern Python and to assume that GitHub Actions will fetch the
appropriate source code locally before the script is run.

Fixes #29206.
Fixes #23798.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

.github/workflows/test-upstream-wpt-changes.yml

@@ -0,0 +1,18 @@
+name: Test changes to upstream-wpt-changes
+on:
+  pull_request:
+    branches: ["**"]
+    paths: ["etc/ci/upstream-wpt-changes/**"]
+
+jobs:
+  test:
+    name: Test
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install dependencies
+        run: |
+          python3 -m pip install --upgrade -r etc/ci/upstream-wpt-changes/requirements-dev.txt
+      - name: Running tests
+        run: |
+          python3 etc/ci/upstream-wpt-changes/test.py

.github/workflows/upstream-wpt-changes.yml

@@ -0,0 +1,34 @@
+# Disabled until the previous bot is turned off.
+#name: Upstream Web Platform Test changes
+#on:
+#  pull_request:
+#    types: ['opened', 'synchronize', 'reopened', 'edited', 'closed']
+#
+#jobs:
+#  upstream:
+#    runs-on: ubuntu-latest
+#    steps:
+#      - name: Calculate PR fetch depth
+#        run: echo "PR_FETCH_DEPTH=$(( ${{ github.event.pull_request.commits }} + 1 ))" >> "${GITHUB_ENV}"
+#      - name: Check out shallow servo PR
+#        run: |
+#          mkdir servo
+#          cd servo
+#          git init -b main
+#          git remote add origin ${{ github.event.repository.clone_url}}
+#          git fetch origin pull/${{ github.event.pull_request.number}}/head:pr --depth ${{ env.PR_FETCH_DEPTH }}
+#          git checkout pr
+#      - name: Check out wpt
+#        uses: actions/checkout@v3
+#        with:
+#          path: wpt
+#          repository: 'web-platform-tests/wpt'
+#          token: ${{ secrets.WPT_UPSTREAM_TOKEN }}
+#      - name: Install requirements
+#        run: pip install -r servo/etc/ci/upstream-wpt-changes/requirements.txt
+#      - name: Process pull request
+#        run: servo/etc/ci/upstream-wpt-changes/upstream-wpt-changes.py
+#        env:
+#          GITHUB_CONTEXT: ${{ toJson(github) }}
+#          GITHUB_TOKEN: ${{ secrets.WPT_UPSTREAM_TOKEN }}
+#