ci: update nix

.github/workflows/nix.yml

@@ -1,20 +1,19 @@
 name: "Nix CI"
 
-on: [pull_request, push]
+on:
+  push:
 
 jobs:
-  tests:
-    name: "Nix build on ${{ matrix.os }}"
+  nix:
     runs-on: "${{ matrix.os }}-latest"
     strategy:
       matrix:
         os: [ubuntu]
     steps:
       - uses: actions/checkout@v4
-      - uses: DeterminateSystems/nix-installer-action@main
-      - uses: DeterminateSystems/magic-nix-cache-action@main
-      - run: nix --accept-flake-config build -L
-      - run: nix --accept-flake-config run .#cachix push gepetto $(readlink result)
-        if: github.repository_owner == 'humanoid-path-planner'
-        env:
-          CACHIX_AUTH_TOKEN: ${{ secrets.CACHIX_AUTH_TOKEN }}
+      - uses: cachix/install-nix-action@v27
+      - uses: cachix/cachix-action@v15
+        with:
+          name: gepetto
+          authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+      - run: nix build