ci: Move nix build to extra-builds.yml

Skip duplicate actions on nix build.

.github/workflows/extra-builds.yml

@@ -81,3 +81,17 @@ jobs:
           END
 
           make -C build -f ../Makefile CXX=clang -j$(nproc)
+
+  nix-build:
+    name: "Build nix flake"
+    needs: pre_job
+    if: needs.pre_job.outputs.should_skip != 'true'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+        submodules: true
+      - uses: cachix/install-nix-action@v26
+        with:
+        install_url: https://releases.nixos.org/nix/nix-2.18.1/install
+      - run: nix build .?submodules=1

.github/workflows/nix-github-actions.yml

@@ -1,15 +0,0 @@
-name: "build nix flake"
-on:
-  pull_request:
-  push:
-jobs:
-  tests:
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@v4
-      with:
-       submodules: true
-    - uses: cachix/install-nix-action@v26
-      with:
-       install_url: https://releases.nixos.org/nix/nix-2.18.1/install
-    - run: nix build .?submodules=1