chore(deps): bump cachix/install-nix-action from 25 to 26

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from 25 to 26.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](cachix/install-nix-action@v25...v26)

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

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

Author: dependabot[bot]

.github/workflows/build-nix.yml

@@ -23,7 +23,7 @@ jobs:
       - uses: actions/checkout@v4
       - name: Setup git lfs
         uses: ./.github/actions/setup-git-lfs
-      - uses: cachix/install-nix-action@v25
+      - uses: cachix/install-nix-action@v26
         with:
           install_url: https://releases.nixos.org/nix/nix-2.13.3/install
           extra_nix_config: |

.github/workflows/update-nix.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v25
+      - uses: cachix/install-nix-action@v26
         with:
           extra_nix_config: |
             access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
@@ -30,7 +30,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v25
+      - uses: cachix/install-nix-action@v26
         with:
           nix_path: nixpkgs=channel:nixos-unstable
           extra_nix_config: |