build(deps): bump cachix/install-nix-action from 31.8.2 to 31.8.4

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from 31.8.2 to 31.8.4.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Changelog](https://github.com/cachix/install-nix-action/blob/master/RELEASE.md)
- [Commits](https://github.com/cachix/install-nix-action/compare/v31.8.2...v31.8.4)

---
updated-dependencies:
- dependency-name: cachix/install-nix-action
  dependency-version: 31.8.4
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

.github/workflows/update-flake.yml

@@ -24,7 +24,7 @@ jobs:
           token: "${{ secrets.GH_TOKEN}}"
 
       - name: "Install Nix"
-        uses: cachix/install-nix-action@v31.8.2
+        uses: cachix/install-nix-action@v31.8.4
 
       - uses: cachix/cachix-action@v16
         with: