Revert "pin flake8 version"

This reverts commit 86ae52b.

.github/workflows/flake8.yaml

@@ -25,7 +25,7 @@ jobs:
     - name: Install flake8
       run: |
         python -m pip install --upgrade pip
-        pip install flake8==6.0.0
+        pip install flake8
     - name: List changed files
       run: |
         git diff --compact-summary "origin/$GITHUB_BASE_REF"