Bump DeterminateSystems/magic-nix-cache-action from 7 to 8

Bumps [DeterminateSystems/magic-nix-cache-action](https://github.com/determinatesystems/magic-nix-cache-action) from 7 to 8.
- [Release notes](https://github.com/determinatesystems/magic-nix-cache-action/releases)
- [Commits](https://github.com/determinatesystems/magic-nix-cache-action/compare/v7...v8)

---
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/build.yml

@@ -39,7 +39,7 @@ jobs:
             experimental-features = pipe-operator
             accept-flake-config = true
 
-      - uses: DeterminateSystems/magic-nix-cache-action@v7
+      - uses: DeterminateSystems/magic-nix-cache-action@v8
 
       - uses: cachix/cachix-action@v15
         with:

.github/workflows/checks.yml

@@ -22,7 +22,7 @@ jobs:
         with:
           extra-conf: |
             accept-flake-config = true
-      - uses: DeterminateSystems/magic-nix-cache-action@v7
+      - uses: DeterminateSystems/magic-nix-cache-action@v8
 
       - uses: cachix/cachix-action@v15
         with: