Bump DeterminateSystems/magic-nix-cache-action from 2 to 7

Bumps [DeterminateSystems/magic-nix-cache-action](https://github.com/determinatesystems/magic-nix-cache-action) from 2 to 7.
- [Release notes](https://github.com/determinatesystems/magic-nix-cache-action/releases)
- [Commits](https://github.com/determinatesystems/magic-nix-cache-action/compare/v2...v7)

---
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

@@ -65,7 +65,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - uses: DeterminateSystems/nix-installer-action@main
-      - uses: DeterminateSystems/magic-nix-cache-action@v2
+      - uses: DeterminateSystems/magic-nix-cache-action@v7
 
       - uses: cachix/cachix-action@v14
         with:

.github/workflows/checks.yml

@@ -33,7 +33,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - uses: DeterminateSystems/nix-installer-action@main
-      - uses: DeterminateSystems/magic-nix-cache-action@v2
+      - uses: DeterminateSystems/magic-nix-cache-action@v7
 
       - uses: cachix/cachix-action@v14
         with: