Bump DeterminateSystems/magic-nix-cache-action from 3 to 4

Bumps [DeterminateSystems/magic-nix-cache-action](https://github.com/determinatesystems/magic-nix-cache-action) from 3 to 4.
- [Release notes](https://github.com/determinatesystems/magic-nix-cache-action/releases)
- [Commits](DeterminateSystems/magic-nix-cache-action@eeabdb0...fc6aace)

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

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/generate.yaml

@@ -28,7 +28,7 @@ jobs:
             access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
 
       - name: Set up magic Nix cache
-        uses: DeterminateSystems/magic-nix-cache-action@eeabdb06718ac63a7021c6132129679a8e22d0c7 # v3
+        uses: DeterminateSystems/magic-nix-cache-action@fc6aaceb40b9845a02b91e059ec147e78d1b4e41 # v4
 
       - name: Prepare Nix shell
         run: nix develop --impure .#ci