Add browser install for playwright

Author: perovskite

.github/workflows/ipywidgets-bokeh-ci.yml

@@ -16,6 +16,7 @@ jobs:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
         node-version: [18.x]
+        browser: [chromium, firefox, webkit]
 
     steps:
       - name: Checkout the repository
@@ -63,6 +64,7 @@ jobs:
         run: |
           python -m pip install --upgrade pip
           python -m pip install --editable .[dev]
+          python -m playwright install --with-deps ${{ matrix.browser }}
 
       - name: Run Playwright & Python tests
         if: success() || failure()