Upgrade: bump cachix/install-nix-action from 24 to 25

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from 24 to 25.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](cachix/install-nix-action@v24...v25)

---
updated-dependencies:
- dependency-name: cachix/install-nix-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/build.yml

@@ -62,7 +62,7 @@ jobs:
         ref: 'main'
 
     - name: 0-3. Install nix
-      uses: cachix/install-nix-action@v24
+      uses: cachix/install-nix-action@v25
       with:
         nix_path: nixpkgs=channel:nixos-unstable
         extra_nix_config: |

.github/workflows/update.yml

@@ -36,7 +36,7 @@ jobs:
       uses: actions/checkout@v4
 
     - name: 0-2. Install nix
-      uses: cachix/install-nix-action@v24
+      uses: cachix/install-nix-action@v25
       with:
         nix_path: nixpkgs=channel:nixos-unstable
         extra_nix_config: |