feat(automation): Add workflow to vendor and update Test262 tests

This commit introduces a GitHub Actions workflow to automate the
vendoring of the Test262 test suite into `third_party/test262`. This
automation is the final piece of the integration, ensuring that the
tests can be kept up-to-date with the upstream `tc39/test262` repository.

The workflow is configured to run weekly or can be triggered manually.
It performs the following steps:
1.  Checks out both the WPT and `tc39/test262` repositories.
2.  Selectively copies a subset of the Test262 tests into WPT.
3.  Copies the essential Test262 harness files.
4.  Creates a `vendored.toml` file at the root of the vendored directory,
    recording the specific commit SHA from `tc39/test262` that the
    files were sourced from. This ensures traceability, as described
    in the RFC.
5.  Commits the updated files and opens a pull request with the changes.

Initially, only a subset of Test262 tests related to Interop 2026
features (`Temporal` and `top-level-await`) are being imported. This is
a temporary measure to manage the volume of new test results and to
avoid overloading wpt.fyi, which currently has limitations in processing
the full Test262 result set (see wpt-fyi/issues/4681). The workflow can
be expanded to include more tests in the future.

This work directly supports the integration of Test262 into WPT as detailed
in the RFC: web-platform-tests/rfcs#229

This commit is part of a series of smaller PRs split from the larger,
original implementation in #55997.

Author: jcscottiii

.github/workflows/update-test262-tests.yml

@@ -0,0 +1,75 @@
+name: Update Test262 tests
+
+on:
+  # Trigger at every Sunday UTC noon, or manually.
+  schedule:
+    - cron: '0 12 * * 0'
+  workflow_dispatch:
+
+jobs:
+  update-test262:
+    runs-on: ubuntu-24.04
+    steps:
+      - name: Checkout WPT repo
+        uses: actions/checkout@v4
+        with:
+          path: wpt
+      - name: Checkout Test262 repo
+        uses: actions/checkout@v4
+        with:
+          repository: tc39/test262
+          path: test262-spec
+      - name: Copy Test262 tests to WPT
+        run: |
+          LATEST_SHA=$(git -C test262-spec rev-parse HEAD)
+          echo "Latest remote Test262 SHA: $LATEST_SHA"
+
+          rm -rf wpt/third_party/test262/test/
+          mkdir -p wpt/third_party/test262/test/
+          mkdir -p wpt/third_party/test262/harness/
+
+          # Selectively copy only Interop 2026 feature tests for now
+          # See: https://github.com/web-platform-tests/wpt.fyi/issues/4681
+          # Mapping of web feature to test directory can be found at: https://github.com/tc39/test262/blob/main/WEB_FEATURES.yml
+          # Temporal tests
+          mkdir -p wpt/third_party/test262/test/built-ins/Date/prototype/toTemporalInstant
+          mkdir -p wpt/third_party/test262/test/built-ins/Temporal
+          mkdir -p wpt/third_party/test262/test/intl402/Temporal
+          cp -r test262-spec/test/built-ins/Date/prototype/toTemporalInstant/* wpt/third_party/test262/test/built-ins/Date/prototype/toTemporalInstant
+          cp -r test262-spec/test/built-ins/Temporal/* wpt/third_party/test262/test/built-ins/Temporal
+          cp -r test262-spec/test/intl402/Temporal/* wpt/third_party/test262/test/intl402/Temporal
+
+          # Top-level-await tests
+          mkdir -p wpt/third_party/test262/test/language/module-code/top-level-await
+          cp -r test262-spec/test/language/module-code/top-level-await/* wpt/third_party/test262/test/language/module-code/top-level-await
+
+          # Always sync the harness files
+          rsync -a --delete test262-spec/harness/ wpt/third_party/test262/harness/
+          printf "[test262]\nsource = \"https://github.com/tc39/test262\"\nrev = \"${LATEST_SHA}\"\n" > wpt/third_party/test262/vendored.toml
+      - name: Commit changes
+        id: commit
+        continue-on-error: true
+        run: |
+          cd wpt
+          export BRANCH_NAME="$BRANCH_PREFIX-$(date +'%Y%m%d%H%M%S')"
+          echo "BRANCH_NAME=$BRANCH_NAME" >> $GITHUB_ENV
+          git config user.name "$GIT_AUTHOR_NAME"
+          git config user.email "$GIT_AUTHOR_EMAIL"
+          git checkout -B $BRANCH_NAME
+          git add third_party/test262/
+          git commit -m "$COMMIT_TITLE"
+        env:
+          GIT_AUTHOR_NAME: "wpt-pr-bot"
+          GIT_AUTHOR_EMAIL: "wpt-pr-bot@users.noreply.github.com"
+          BRANCH_PREFIX: "test262-update"
+          COMMIT_TITLE: "Update Test262 tests"
+      - name: Create PR
+        if: ${{ steps.commit.outcome == 'success' }}
+        run: |
+          cd wpt
+          git push --set-upstream origin $BRANCH_NAME
+          gh pr create --title "$COMMIT_TITLE" --body "$PR_BODY"
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          COMMIT_TITLE: "Update Test262 tests"
+          PR_BODY: "Scheduled weekly update auto-generated by the '${{ github.workflow }}' workflow."