fix(ci): Remove nix cache action as it barely works

It takes 11 minutes to cache everything on a otherwise 2 minute job.
Nix doesn't even pull from it most of the time.

.github/workflows/check.yml

@@ -42,8 +42,6 @@ jobs:
       - uses: actions/checkout@v4
       - name: Install nix
         uses: https://github.com/DeterminateSystems/nix-installer-action@main
-      - name: Setup Action cache for nix
-        uses: https://github.com/DeterminateSystems/magic-nix-cache-action@main
         with:
           fail-mode: true
       - name: Check Nix flake inputs