Add --config option to flake8 command in CI workflow

Before the latest release of flake8, the configuration file was automatically loaded, but the program's behavior has changed.

Author: per1234

.github/workflows/libraries_report-size-deltas.yml

@@ -33,7 +33,7 @@ jobs:
         run: |
           pip install --quiet flake8
           pip install --quiet pep8-naming
-          flake8 --show-source "$GITHUB_WORKSPACE/libraries/report-size-deltas"
+          flake8 --config "$GITHUB_WORKSPACE/libraries/report-size-deltas/.flake8" --show-source "$GITHUB_WORKSPACE/libraries/report-size-deltas"
 
       - name: Run Python unit tests
         run: |