chore(ci)(deps): bump DeterminateSystems/magic-nix-cache-action

Bumps [DeterminateSystems/magic-nix-cache-action](https://github.com/determinatesystems/magic-nix-cache-action) from 3 to 6.
- [Release notes](https://github.com/determinatesystems/magic-nix-cache-action/releases)
- [Commits](DeterminateSystems/magic-nix-cache-action@v3...v6)

---
updated-dependencies:
- dependency-name: DeterminateSystems/magic-nix-cache-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/nix.yml

@@ -18,7 +18,7 @@ jobs:
         uses: DeterminateSystems/nix-installer-action@v9
 
       - name: Cache Magic
-        uses: DeterminateSystems/magic-nix-cache-action@v3
+        uses: DeterminateSystems/magic-nix-cache-action@v6
 
       - name: Check Nix flake inputs
         uses: DeterminateSystems/flake-checker-action@v5