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/nix.yml

@@ -17,7 +17,7 @@ jobs:
         with:
           submodules: recursive
 
-      - uses: cachix/install-nix-action@v30
+      - uses: cachix/install-nix-action@v31
         with:
           nix_path: nixpkgs=channel:nixos-unstable
 
@@ -32,7 +32,7 @@ jobs:
         with:
           submodules: recursive
 
-      - uses: cachix/install-nix-action@v30
+      - uses: cachix/install-nix-action@v31
         with:
           nix_path: nixpkgs=channel:nixos-unstable
 
@@ -46,7 +46,7 @@ jobs:
         with:
           submodules: recursive
 
-      - uses: cachix/install-nix-action@v30
+      - uses: cachix/install-nix-action@v31
         with:
           nix_path: nixpkgs=channel:nixos-unstable