ci(deps): bump actions/setup-python from 5 to 6 (#215)

Author: dependabot[bot]

.github/workflows/self-test.yml

@@ -36,7 +36,7 @@ jobs:
             devpi
 
       - name: Set up Python
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@v6
         id: setup-python
         with:
           python-version: '3.13'