Update python-stylecheck action with required checkout modifier

Pull in required commits for the CHANGED_FILES check like in the upstream example.

Signed-off-by: Jonas Bardino <bardino@science.ku.dk>

Author: jonasbardino

.github/workflows/python-stylecheck.yml

@@ -17,6 +17,8 @@ jobs:
     steps:
       - name: Check out source repository
         uses: actions/checkout@v4
+        with:
+          fetch-depth: 0  # This is necessary to get the commits
       - name: Get changed python files between base and head
         run: >
           echo "CHANGED_FILES=$(echo $(git diff --name-only ${{ github.event.pull_request.base.sha }}..${{ github.event.pull_request.head.sha }} -- | grep \.py))" >> $GITHUB_ENV