build(deps): Bump DeterminateSystems/nix-installer-action from 14 to 15

Bumps [DeterminateSystems/nix-installer-action](https://github.com/determinatesystems/nix-installer-action) from 14 to 15.
- [Release notes](https://github.com/determinatesystems/nix-installer-action/releases)
- [Commits](DeterminateSystems/nix-installer-action@v14...v15)

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

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

.github/workflows/ci.yaml

@@ -18,7 +18,7 @@ jobs:
       matrix: ${{ steps.set-matrix.outputs.matrix }}
     steps:
       - uses: actions/checkout@v4
-      - uses: DeterminateSystems/nix-installer-action@v14
+      - uses: DeterminateSystems/nix-installer-action@v15
       - uses: DeterminateSystems/magic-nix-cache-action@v8
       - id: set-matrix
         name: Generate Nix Matrix
@@ -37,7 +37,7 @@ jobs:
       matrix: ${{ fromJSON(needs.nix-matrix.outputs.matrix) }}
     steps:
       - uses: actions/checkout@v4
-      - uses: DeterminateSystems/nix-installer-action@v14
+      - uses: DeterminateSystems/nix-installer-action@v15
       - uses: DeterminateSystems/magic-nix-cache-action@v8
       - run: nix build -L ".#${{ matrix.attr }}" --keep-going