Build: Only install Playwright dependencies when needed

PR jquerygh-5190 added support for running tests on Playwright WebKit
in CI. For efficiency reasons, Playwright dependencies are only
installed for the `test:browser` npm script. However, that same
script is also used for Firefox ESR testing.

This change makes Playwright dependencies installed only for cases
where `WebKitHeadless` exists on the list of tested browsers.

Closes jquerygh-5204
Ref jquerygh-5190

.github/workflows/node.js.yml

@@ -73,7 +73,7 @@ jobs:
 
     - name: Install Playwright dependencies
       run: npx playwright-webkit install-deps
-      if: "matrix.NPM_SCRIPT == 'test:browser'"
+      if: "matrix.NPM_SCRIPT == 'test:browser' && contains(matrix.BROWSERS, 'WebkitHeadless')"
 
     - name: Run tests
       env: