Maybe fixed cppcheck diff

Author: oddbookworm

.github/workflows/run-ubuntu-checks.yml

@@ -140,6 +140,7 @@ jobs:
       id: check-changes
       run: |
         git fetch origin ${{ github.base_ref }} --depth=1 || true
+        git checkout ${{ github.base_ref }}
         CHANGED_FILES=$(git diff --name-only origin/${{ github.base_ref }}...HEAD)
         echo "$CHANGED_FILES" | grep '^src_c/' || echo "::set-output name=skip::true"