Bump DeterminateSystems/nix-installer-action from 7 to 8 (#42)

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

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

.github/workflows/build-slides.yml

@@ -26,7 +26,7 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Install Nix
-        uses: DeterminateSystems/nix-installer-action@v7
+        uses: DeterminateSystems/nix-installer-action@v8
 
       - name: Cache Nix artifacts
         uses: DeterminateSystems/magic-nix-cache-action@v2

.github/workflows/release-slides.yml

@@ -22,7 +22,7 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Install Nix
-        uses: DeterminateSystems/nix-installer-action@v7
+        uses: DeterminateSystems/nix-installer-action@v8
 
       - name: Cache Nix artifacts
         uses: DeterminateSystems/magic-nix-cache-action@v2