Bump DeterminateSystems/nix-installer-action from 4 to 6

Bumps [DeterminateSystems/nix-installer-action](https://github.com/determinatesystems/nix-installer-action) from 4 to 6.
- [Release notes](https://github.com/determinatesystems/nix-installer-action/releases)
- [Commits](https://github.com/determinatesystems/nix-installer-action/compare/v4...v6)

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

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

.github/workflows/build-iso.yml

@@ -22,7 +22,7 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
     - uses: actions/checkout@v4
-    - uses: DeterminateSystems/nix-installer-action@v4
+    - uses: DeterminateSystems/nix-installer-action@v6
     - uses: DeterminateSystems/magic-nix-cache-action@v2
     - name: Build Console ISO
       run: |
@@ -46,7 +46,7 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
     - uses: actions/checkout@v4
-    - uses: DeterminateSystems/nix-installer-action@v4
+    - uses: DeterminateSystems/nix-installer-action@v6
     - uses: DeterminateSystems/magic-nix-cache-action@v2
     - name: Build Desktop ISO
       run: |

.github/workflows/deadnix.yml

@@ -11,6 +11,6 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v4
-      - uses: DeterminateSystems/nix-installer-action@v4
+      - uses: DeterminateSystems/nix-installer-action@v6
       - uses: DeterminateSystems/magic-nix-cache-action@v2
       - uses: astro/deadnix-action@v1

.github/workflows/flake-checker.yml

@@ -17,6 +17,6 @@ jobs:
       - uses: actions/checkout@v4
         with:
           fetch-depth: 0
-      - uses: DeterminateSystems/nix-installer-action@v4
+      - uses: DeterminateSystems/nix-installer-action@v6
       - uses: DeterminateSystems/magic-nix-cache-action@v2
       - uses: DeterminateSystems/flake-checker-action@v5

.github/workflows/lock-updater.yml

@@ -14,7 +14,7 @@ jobs:
       - uses: actions/checkout@v4
         with:
           fetch-depth: 0
-      - uses: DeterminateSystems/nix-installer-action@v4
+      - uses: DeterminateSystems/nix-installer-action@v6
       - uses: DeterminateSystems/magic-nix-cache-action@v2
       - uses: DeterminateSystems/update-flake-lock@v20
         with: