Fix and simplify CodeQL workflow

Warning: 1 issue was detected with this workflow: git checkout HEAD^2 is no longer necessary. Please remove this step as Code Scanning recommends analyzing the merge commit for best results.

.github/workflows/codeql-analysis.yml

@@ -19,33 +19,15 @@ jobs:
     name: Analyze
     runs-on: ubuntu-latest
 
-    strategy:
-      fail-fast: false
-      matrix:
-        # Override automatic language detection by changing the below list
-        # Supported options are ['csharp', 'cpp', 'go', 'java', 'javascript', 'python']
-        language: ['python']
-        # Learn more...
-        # https://docs.github.com/en/github/finding-security-vulnerabilities-and-errors-in-your-code/configuring-code-scanning#overriding-automatic-language-detection
-
     steps:
     - name: Checkout repository
       uses: actions/checkout@v2
-      with:
-        # We must fetch at least the immediate parents so that if this is
-        # a pull request then we can checkout the head.
-        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' }}
 
     # Initializes the CodeQL tools for scanning.
     - name: Initialize CodeQL
       uses: github/codeql-action/init@v1
       with:
-        languages: ${{ matrix.language }}
+        languages: python
         # If you wish to specify custom queries, you can do so here or in a config file.
         # By default, queries listed here will override any specified in a config file.
         # Prefix the list here with "+" to use these queries and those in the config file.