Try to use nixos host runner

.gitea/workflows/build.yaml

@@ -16,19 +16,11 @@ env:
 jobs:
   build-and-push:
     # We use the standard ubuntu-latest to build our custom runner
-    runs-on: ubuntu-latest 
+    runs-on: nixos
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
 
-      # --- Lower MTU to prevent packet drops on large Nix layers ---
-      - name: Adjust MTU to fix Docker push timeouts
-        run: |
-          # Find the active network interface and lower its MTU
-          INTERFACE=$(ip route | grep default | awk '{print $5}')
-          echo "Lowering MTU on interface: $INTERFACE"
-          sudo ip link set dev $INTERFACE mtu 1400
-
       # Gitea Actions automatically provides a token that can push to its own registry
       - name: Log in to the Container registry
         uses: docker/login-action@v3