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/latexmk.yaml

@@ -12,7 +12,7 @@ jobs:
       uses: DeterminateSystems/nix-installer-action@v13
       with:
         github-token: ${{ secrets.GITHUB_TOKEN }}
-    - uses: DeterminateSystems/magic-nix-cache-action@v7
+    - uses: DeterminateSystems/magic-nix-cache-action@v8
     - run: nix build -o cv.pdf
     - name: Release
       uses: softprops/action-gh-release@v2