ci: bump cachix/cachix-action from 15 to 16

Bumps [cachix/cachix-action](https://github.com/cachix/cachix-action) from 15 to 16.
- [Release notes](https://github.com/cachix/cachix-action/releases)
- [Commits](https://github.com/cachix/cachix-action/compare/v15...v16)

---
updated-dependencies:
- dependency-name: cachix/cachix-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/check.yml

@@ -18,7 +18,7 @@ jobs:
     steps:
       - uses: DeterminateSystems/nix-installer-action@v16
 
-      - uses: cachix/cachix-action@v15
+      - uses: cachix/cachix-action@v16
         with:
           name: stylix
           authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
@@ -90,7 +90,7 @@ jobs:
               'false'
             }}
 
-      - uses: cachix/cachix-action@v15
+      - uses: cachix/cachix-action@v16
         with:
           name: stylix
           authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'

.github/workflows/docs.yml

@@ -28,7 +28,7 @@ jobs:
 
       - uses: DeterminateSystems/nix-installer-action@v16
 
-      - uses: cachix/cachix-action@v15
+      - uses: cachix/cachix-action@v16
         with:
           name: stylix
           authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'