build(deps): bump the actions group with 2 updates

Bumps the actions group with 2 updates: [DeterminateSystems/nix-installer-action](https://github.com/determinatesystems/nix-installer-action) and [DeterminateSystems/magic-nix-cache-action](https://github.com/determinatesystems/magic-nix-cache-action).


Updates `DeterminateSystems/nix-installer-action` from 11 to 12
- [Release notes](https://github.com/determinatesystems/nix-installer-action/releases)
- [Commits](DeterminateSystems/nix-installer-action@v11...v12)

Updates `DeterminateSystems/magic-nix-cache-action` from 6 to 7
- [Release notes](https://github.com/determinatesystems/magic-nix-cache-action/releases)
- [Commits](DeterminateSystems/magic-nix-cache-action@v6...v7)

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

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/nix.yaml

@@ -21,8 +21,8 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - name: Install Nix
-        uses: DeterminateSystems/nix-installer-action@v11
+        uses: DeterminateSystems/nix-installer-action@v12
       - name: Setup Nix Cache
-        uses: DeterminateSystems/magic-nix-cache-action@v6
+        uses: DeterminateSystems/magic-nix-cache-action@v7
       - run: nix build
       - run: nix flake check