fix: replace actions/checkout with git clone in nix-update workflow

- Remove dependency on Node.js for checkout action
- Use direct git clone with auth token
- Fixes: nixpkgs-5yn

.gitea/workflows/nix-update.yml

@@ -21,10 +21,8 @@ jobs:
     runs-on: nixos
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v4
-        with:
-          fetch-depth: 0
-          token: ${{ secrets.NIX_UPDATE_TOKEN }}
+        run: |
+          git clone --depth 0 ${{ secrets.NIX_UPDATE_TOKEN }}@${{ github.server_url }}/${{ github.repository }}.git .
 
       - name: Check for available packages to update
         id: check-packages