ci: run the Chrome-driven browser suite in a separate job

.github/workflows/ci.yml

@@ -83,3 +83,20 @@ jobs:
 
       - name: Run tests
         run: make test
+
+  browser:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+          cache: true
+
+      - name: Set up Chrome
+        uses: browser-actions/setup-chrome@v1
+
+      - name: Drive web fixtures through headless Chrome
+        run: make test-browser