config(.github/ci): Use relative path for the install-nix job

Author: MartinNikov

.github/workflows/ci.yml

@@ -27,7 +27,7 @@ jobs:
     runs-on: self-hosted
     steps:
       - name: Install Nix
-        uses: metacraft-labs/nixos-modules/.github/install-nix@main
+        uses: ./../install-nix
         with:
           cachix-cache: ${{ vars.CACHIX_CACHE }}
           cachix-auth-token: ${{ secrets.CACHIX_AUTH_TOKEN }}