build(deps): bump cachix/install-nix-action from 17 to 18 (helix-editor#4340)

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/cachix.yml

@@ -14,7 +14,7 @@ jobs:
       uses: actions/checkout@v3
 
     - name: Install nix
-      uses: cachix/install-nix-action@v17
+      uses: cachix/install-nix-action@v18
 
     - name: Authenticate with Cachix
       uses: cachix/cachix-action@v11