build(deps): 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](cachix/cachix-action@v14...v15)

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

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

Author: dependabot[bot]

.github/workflows/deadnix.yml

@@ -9,7 +9,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: cachix/install-nix-action@v29
-      - uses: cachix/cachix-action@v14
+      - uses: cachix/cachix-action@v15
         with:
           name: deadnix
       - uses: astro/deadnix-action@main

.github/workflows/prebuilt-23.05.yml

@@ -14,7 +14,7 @@ jobs:
     steps:
     - uses: actions/checkout@v4
     - uses: cachix/install-nix-action@v29
-    - uses: cachix/cachix-action@v14
+    - uses: cachix/cachix-action@v15
       with:
         name: microvm
         authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'

.github/workflows/prebuilt-23.11.yml

@@ -14,7 +14,7 @@ jobs:
     steps:
     - uses: actions/checkout@v4
     - uses: cachix/install-nix-action@v29
-    - uses: cachix/cachix-action@v14
+    - uses: cachix/cachix-action@v15
       with:
         name: microvm
         authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'

.github/workflows/prebuilt-unstable.yml

@@ -14,7 +14,7 @@ jobs:
     steps:
     - uses: actions/checkout@v4
     - uses: cachix/install-nix-action@v29
-    - uses: cachix/cachix-action@v14
+    - uses: cachix/cachix-action@v15
       with:
         name: microvm
         authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'

.github/workflows/prebuilt.yml

@@ -14,7 +14,7 @@ jobs:
     steps:
     - uses: actions/checkout@v4
     - uses: cachix/install-nix-action@v29
-    - uses: cachix/cachix-action@v14
+    - uses: cachix/cachix-action@v15
       with:
         name: microvm
         authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'