Bump cachix/install-nix-action from 24 to 25

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from 24 to 25.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](cachix/install-nix-action@7ac1ec2...6004951)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/CI.yml

@@ -16,7 +16,7 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11
-      - uses: cachix/install-nix-action@7ac1ec25491415c381d9b62f0657c7a028df52a7
+      - uses: cachix/install-nix-action@6004951b182f8860210c8d6f0d808ec5b1a33d28
       - name: Build
         run: nix-shell --pure --run 'make SPHINXOPTS='-W' html'
   build_docker_image_theme_tuleap_org: