Only run Node 14 tests on merge commits of pull requests

The "pull_request" workflow acts more as a "sanity check"
that the PR branch is sufficiently up-to-date with the base branch.

We leave the real heavy lifting over to the "push" workflow.

.github/workflows/pull-request.yml

@@ -5,7 +5,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node-version: [12, 14]
+        node-version: [14]
     # Run only on non-merged non-draft mergeable pull requests
     if: |
       !(
@@ -32,33 +32,3 @@ jobs:
       - run: npm run test:unit
       - run: npm run test:wpt:node
       - run: npm run test:bundler
-
-  test-browser:
-    runs-on: ubuntu-latest
-    strategy:
-      fail-fast: false
-      matrix:
-        browser: [chromium, firefox]
-    if: |
-      !(
-        (github.event.action == 'opened' || github.event.action == 'reopened' || github.event.action == 'synchronize')
-        && !github.event.pull_request.draft
-        && !github.event.pull_request.merged
-        && github.event.pull_request.merge_commit_sha != null
-      )
-    steps:
-      - name: Check out merge commit of pull request
-        uses: actions/checkout@v2
-        with:
-          ref: ${{ github.event.pull_request.merge_commit_sha }}
-          submodules: true
-      - name: Use Node.js 14
-        uses: actions/setup-node@v2
-        with:
-          node-version: 14
-          cache: npm
-      - run: npm ci
-        env:
-          PLAYWRIGHT_SKIP_BROWSER_DOWNLOAD: 1
-      - run: npx playwright install --with-deps ${{ matrix.browser }}
-      - run: npm run test:wpt:${{ matrix.browser }}