Fix warning about git checkout HEAD^2 (#3829)

Currently CI is warning that this step is no longer needed, so remove
it.

.github/workflows/codeql-analysis.yml

@@ -14,11 +14,6 @@ jobs:
         # 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