Build: Separate the install step from running tests in GitHub Actions

Also, update the "Run test" label to "Run tests".

Closes gh-4992

.github/workflows/node.js.yml

@@ -59,10 +59,13 @@ jobs:
         wget --no-verbose $FIREFOX_SOURCE_URL -O - | tar -jx -C ${HOME}
       if: "contains(matrix.NAME, 'Firefox ESR')"
 
-    - name: Run test
+    - name: Install dependencies
+      run: |
+        npm install
+
+    - name: Run tests
       env:
         BROWSERS: ${{ matrix.BROWSERS }}
       run: |
         export PATH=${HOME}/firefox:$PATH
-        npm install
         npm run ${{ matrix.NPM_SCRIPT }}