Bump cachix/install-nix-action from 20 to 30

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from 20 to 30.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](cachix/install-nix-action@v20...v30)

---
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]>

.github/workflows/check.yml

@@ -11,7 +11,7 @@ jobs:
     - name: Checkout
       uses: actions/checkout@v3
     - name: Install nixFlake
-      uses: cachix/install-nix-action@v20
+      uses: cachix/install-nix-action@v30
       with:
         install_url: https://github.com/numtide/nix-unstable-installer/releases/latest/download/install
         extra_nix_config: |

.github/workflows/update.yml

@@ -17,7 +17,7 @@ jobs:
         # Nix Flakes doesn't work on shallow clones
         fetch-depth: 0
     - name: Install nixFlake
-      uses: cachix/install-nix-action@v20
+      uses: cachix/install-nix-action@v30
       with:
         install_url: https://github.com/numtide/nix-unstable-installer/releases/latest/download/install
         extra_nix_config: |