refac: format backend ci

.github/workflows/format-backend.yaml

 name: Python CI
+
 on:
   push:
     branches: ['main']
   pull_request:
+
 jobs:
   build:
     name: 'Format Backend'
-    env:
-      PUBLIC_API_BASE_URL: ''
     runs-on: ubuntu-latest
+
     strategy:
       matrix:
-        node-version:
-          - latest
+        python-version: [3.11]
+
     steps:
       - uses: actions/checkout@v4
-      - name: Use Python
-        uses: actions/setup-python@v4
-      - name: Use Bun
-        uses: oven-sh/setup-bun@v1
+
+      - name: Set up Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: ${{ matrix.python-version }}
+
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
           pip install black
+
       - name: Format backend
-        run: bun run format:backend
+        run: black . --exclude "/venv/"
+
       - name: Check for changes after format
         run: git diff --exit-code