update tests to exercise root action

.github/workflows/codeql.yml

@@ -26,3 +26,26 @@ jobs:
         languages: javascript
         config-file: ./.github/codeql/codeql-config.yml
     - uses: ./analyze
+  
+  test-root-action:
+    strategy:
+      matrix:
+        os: [ubuntu-latest,windows-latest,macos-latest]
+    runs-on: ${{ matrix.os }}
+
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        # Must fetch at least the immediate parents so that if this is
+        # a pull request then we can checkout the head of the pull request.
+        fetch-depth: 2
+
+    # If this run was triggered by a pull request event then checkout
+    # the head of the pull request instead of the merge commit.
+    - run: git checkout HEAD^2
+      if: ${{ github.event_name == 'pull_request' }}
+
+    - uses: github/codeql-action@${{ 'testing_testing' }}
+      with:
+        languages: javascript
+        config-file: ./.github/codeql/codeql-config.yml