Bump the nix-actions group with 2 updates (#259)

Bumps the nix-actions group with 2 updates: [DeterminateSystems/nix-installer-action](https://github.com/determinatesystems/nix-installer-action) and [DeterminateSystems/magic-nix-cache-action](https://github.com/determinatesystems/magic-nix-cache-action).


Updates `DeterminateSystems/nix-installer-action` from 13 to 14
- [Release notes](https://github.com/determinatesystems/nix-installer-action/releases)
- [Commits](DeterminateSystems/nix-installer-action@v13...v14)

Updates `DeterminateSystems/magic-nix-cache-action` from 7 to 8
- [Release notes](https://github.com/determinatesystems/magic-nix-cache-action/releases)
- [Commits](DeterminateSystems/magic-nix-cache-action@v7...v8)

---
updated-dependencies:
- dependency-name: DeterminateSystems/nix-installer-action
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: nix-actions
- dependency-name: DeterminateSystems/magic-nix-cache-action
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: nix-actions
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/ci-nix.yml

@@ -26,8 +26,8 @@ jobs:
     timeout-minutes: 30
     steps:
       - uses: actions/checkout@v4
-      - uses: DeterminateSystems/nix-installer-action@v13
-      - uses: DeterminateSystems/magic-nix-cache-action@v7
+      - uses: DeterminateSystems/nix-installer-action@v14
+      - uses: DeterminateSystems/magic-nix-cache-action@v8
       - run: nix flake check
       - run: nix develop --command echo 'This step should be done before any other "nix develop" steps because of measuring Nix build time'
       - run: nix develop --command bundle install