build(deps): bump cachix/install-nix-action from 31.8.4 to 31.9.0

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from 31.8.4 to 31.9.0.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Changelog](https://github.com/cachix/install-nix-action/blob/master/RELEASE.md)
- [Commits](cachix/install-nix-action@v31.8.4...v31.9.0)

---
updated-dependencies:
- dependency-name: cachix/install-nix-action
  dependency-version: 31.9.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

.github/workflows/test.yml

@@ -6,7 +6,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v6
-    - uses: cachix/install-nix-action@v31.8.4
+    - uses: cachix/install-nix-action@v31.9.0
       with:
         extra_nix_config: |
           access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}

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

@@ -11,7 +11,7 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v6
       - name: Install Nix
-        uses: cachix/install-nix-action@v31.8.4
+        uses: cachix/install-nix-action@v31.9.0
         with:
           extra_nix_config: |
             access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}