build(deps): bump cachix/install-nix-action from V27 to 29

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from V27 to 29. This release includes the previously tagged commit.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](cachix/install-nix-action@V27...v29)

---
updated-dependencies:
- dependency-name: cachix/install-nix-action
  dependency-type: direct:production
...

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

Author: dependabot[bot]

.github/workflows/integrationtest.yml

@@ -26,7 +26,7 @@ jobs:
     steps:
       - name: Check out
         uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@V27
+      - uses: cachix/install-nix-action@v29
         with:
           # This channel is only required to invoke "nix-shell".
           # Everything inside that nix-shell will use a pinned version of