fix: streamline build workflow by removing unnecessary steps

.gitea/workflows/build.yaml

@@ -9,30 +9,23 @@ jobs:
   build:
     runs-on: self-hosted
     steps:
-      # 1. Git Repository aktualisieren
-      - name: Update repository
-        run: |
-          git reset --hard
-          git pull
+      - name: Checkout code
+        uses: actions/checkout@v3
 
-      # 2. Frontend bauen
       - name: Build Frontend
         run: |
           cd frontend
           npm install
           npm run build
 
-      # 3. Backend Dependencies
       - name: Setup Backend
         run: |
           cd backend
           python3 -m venv venv
           source venv/bin/activate
-          pip install --upgrade pip
           pip install -r requirements.txt
           deactivate
 
-      # 4. Backend neu starten
       - name: Restart Backend
         run: |
           sudo systemctl restart mitm-backend