build(deps): bump DeterminateSystems/nix-installer-action from 9 to 21

Bumps [DeterminateSystems/nix-installer-action](https://github.com/determinatesystems/nix-installer-action) from 9 to 21.
- [Release notes](https://github.com/determinatesystems/nix-installer-action/releases)
- [Commits](DeterminateSystems/nix-installer-action@v9...v21)

---
updated-dependencies:
- dependency-name: DeterminateSystems/nix-installer-action
  dependency-version: '21'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/update-flake-lock.yml

@@ -10,7 +10,7 @@ jobs:
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
-      - uses: DeterminateSystems/nix-installer-action@v9
+      - uses: DeterminateSystems/nix-installer-action@v21
       - name: Update flake.lock
         uses: DeterminateSystems/update-flake-lock@v20
         with: