build(deps): bump cachix/install-nix-action from 30 to 31

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from 30 to 31.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](cachix/install-nix-action@v30...v31)

---
updated-dependencies:
- dependency-name: cachix/install-nix-action
  dependency-version: '31'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/cachix.yml

@@ -15,7 +15,7 @@ jobs:
       uses: actions/checkout@v4
 
     - name: Install nix
-      uses: cachix/install-nix-action@v30
+      uses: cachix/install-nix-action@v31
 
     - name: Authenticate with Cachix
       uses: cachix/cachix-action@v15