Bump cachix/install-nix-action from V28 to 29

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from V28 to 29. This release includes the previously tagged commit.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](cachix/install-nix-action@V28...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/ci.yml

@@ -281,7 +281,7 @@ jobs:
           cache: yarn
           cache-dependency-path: './docs/website/yarn.lock'
 
-      - uses: cachix/install-nix-action@V28
+      - uses: cachix/install-nix-action@v29
         with:
           extra_nix_config: |
             accept-flake-config = true

.github/workflows/documentation.yml

@@ -33,7 +33,7 @@ jobs:
           cache: yarn
           cache-dependency-path: './docs/website/yarn.lock'
 
-      - uses: cachix/install-nix-action@V28
+      - uses: cachix/install-nix-action@v29
         with:
           extra_nix_config: |
             accept-flake-config = true