build(deps): 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](DeterminateSystems/magic-nix-cache-action@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] <[email protected]>

.github/workflows/ci.yml

@@ -18,7 +18,7 @@ jobs:
     steps:
     - uses: actions/checkout@v4
     - uses: cachix/install-nix-action@v27
-    - uses: DeterminateSystems/magic-nix-cache-action@v7
+    - uses: DeterminateSystems/magic-nix-cache-action@v8
     - run: nix run github:Mic92/nix-fast-build -- --no-nom
   # all builds combined consume too much disk space... we should soon switch to something else
   nixos:
@@ -32,5 +32,5 @@ jobs:
     steps:
     - uses: actions/checkout@v4
     - uses: cachix/install-nix-action@v27
-    - uses: DeterminateSystems/magic-nix-cache-action@v7
+    - uses: DeterminateSystems/magic-nix-cache-action@v8
     - run: nix build '.#nixosConfigurations."${{ matrix.machine }}.nixos.org".config.system.build.toplevel'