Bump cachix/cachix-action from 14 to 15

Bumps [cachix/cachix-action](https://github.com/cachix/cachix-action) from 14 to 15.
- [Release notes](https://github.com/cachix/cachix-action/releases)
- [Commits](https://github.com/cachix/cachix-action/compare/v14...v15)

---
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/build.yaml

@@ -50,7 +50,7 @@ jobs:
           github-token: ${{ secrets.GITHUB_TOKEN }}
           extra-conf: "system-features = nixos-test benchmark big-parallel kvm"
       - name: Setup Caching
-        uses: cachix/cachix-action@v14
+        uses: cachix/cachix-action@v15
         with:
           name: selfhostblocks
           authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
@@ -77,7 +77,7 @@ jobs:
           github-token: ${{ secrets.GITHUB_TOKEN }}
           extra-conf: "system-features = nixos-test benchmark big-parallel kvm"
       - name: Setup Caching
-        uses: cachix/cachix-action@v14
+        uses: cachix/cachix-action@v15
         with:
           name: selfhostblocks
           authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
@@ -104,7 +104,7 @@ jobs:
           github-token: ${{ secrets.GITHUB_TOKEN }}
           extra-conf: "system-features = nixos-test benchmark big-parallel kvm"
       - name: Setup Caching
-        uses: cachix/cachix-action@v14
+        uses: cachix/cachix-action@v15
         with:
           name: selfhostblocks
           authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'

.github/workflows/demo.yml

@@ -52,7 +52,7 @@ jobs:
       - name: Install nix
         uses: cachix/install-nix-action@v30
 
-      - uses: cachix/cachix-action@v14
+      - uses: cachix/cachix-action@v15
         with:
           name: selfhostblocks
           authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'

.github/workflows/pages.yml

@@ -35,7 +35,7 @@ jobs:
         uses: cachix/install-nix-action@v30
 
       - name: Setup Caching
-        uses: cachix/cachix-action@v14
+        uses: cachix/cachix-action@v15
         with:
           name: selfhostblocks
           authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'