updated nix action to v30

.gitea/workflows/nix-check.yaml

@@ -1,19 +1,12 @@
-name: Verify Nix Flake Build
-
-on:
-  push:
-    branches: [master]
-  pull_request:
-    branches: [master]
+name: Verify Nix Flake
+run-name: ${{ gitea.actor }} is nix-check
+on: [push]
 
 jobs:
   verify_build:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - name: Install Nix
-        uses: cachix/install-nix-action@v2
-        with:
-          nix_version: '2.18.1'
+      - uses: cachix/install-nix-action@v30
       - name: Verify Nix Flake
-        run: nix flake check
+      - run: nix flake check