Bump DeterminateSystems/nix-installer-action from 11 to 12 (#356)

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

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/flake-update.yml

@@ -11,7 +11,7 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v4.1.6
       - name: Install Nix
-        uses: DeterminateSystems/nix-installer-action@v11
+        uses: DeterminateSystems/nix-installer-action@v12
       - name: Update flake lock
         id: update
         uses: DeterminateSystems/update-flake-lock@v22