ci: use self-hosted nixos runner and change schedule to daily

.gitea/workflows/nix-update.yml

@@ -2,7 +2,7 @@ name: Update Nix Packages with nix-update
 
 on:
   schedule:
-    - cron: '@weekly'
+    - cron: '0 2 * * *'
   workflow_dispatch:  # Allow manual triggering
     inputs:
       package:
@@ -18,7 +18,7 @@ env:
 
   jobs:
   nix-update:
-    runs-on: ubuntu-latest
+    runs-on: nixos
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
@@ -26,21 +26,6 @@ jobs:
           fetch-depth: 0
           token: ${{ secrets.NIX_UPDATE_TOKEN }}
 
-      - name: Install Nix
-        uses: https://github.com/cachix/install-nix-action@v31
-        with:
-          extra_nix_config: |
-            experimental-features = nix-command flakes
-            sandbox = false
-
-      - name: Configure Nix
-        run: |
-          mkdir -p ~/.config/nix
-          cat >> ~/.config/nix/nix.conf << EOF
-            experimental-features = nix-command flakes
-            sandbox = false
-          EOF
-
       - name: Check for available packages to update
         id: check-packages
         run: |