Add ctags installation step to GitHub Actions workflow

.github/workflows/testing.yml

@@ -20,6 +20,8 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         pip install pylint pycodestyle colorama pytest pytest-mock
+    - name: Install ctags
+      run: sudo apt-get update && sudo apt-get install -y exuberant-ctags
     - name: Create test-results directory
       run: mkdir -p test-results
     - name: Test with pytest