ci: replace pipx calls with community actions

.forgejo/workflows/ci.yml

@@ -21,12 +21,13 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
-      - name: Install pipx
-        run: pip install pipx
       - name: Check formatting
-        run: pipx run black . --check
+        uses: https://github.com/psf/black@stable
+        with:
+          options: "--check --verbose"
+          version: "~= 24.0"
       - name: Check import ordering
-        run: pipx run isort . --check
+        uses: https://github.com/isort/isort-action@v1
   post-run-notify:
     runs-on: ubuntu-latest
     if: always()