⬆️ Bump cachix/install-nix-action from 25 to 30

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from 25 to 30.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](https://github.com/cachix/install-nix-action/compare/v25...v30)

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

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

.github/workflows/ci.yml

@@ -492,7 +492,7 @@ jobs:
 
       # I could not find a way to install tree-grepper without nix
       # https://github.com/BrianHicks/tree-grepper/issues/293
-      - uses: cachix/install-nix-action@v25
+      - uses: cachix/install-nix-action@v30
       - uses: cachix/cachix-action@v14
         with:
             name: tree-grepper