Bump seanmiddleditch/gha-setup-ninja from 5 to 6

Bumps [seanmiddleditch/gha-setup-ninja](https://github.com/seanmiddleditch/gha-setup-ninja) from 5 to 6.
- [Release notes](https://github.com/seanmiddleditch/gha-setup-ninja/releases)
- [Commits](seanmiddleditch/gha-setup-ninja@v5...v6)

---
updated-dependencies:
- dependency-name: seanmiddleditch/gha-setup-ninja
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/nightly.yml

@@ -37,7 +37,7 @@ jobs:
       # This must happen after checking out the repository, because Ninja gets installed
       # in the repository's directory that gets removed before the checkout/
       - name: Install Ninja
-        uses: seanmiddleditch/gha-setup-ninja@v5
+        uses: seanmiddleditch/gha-setup-ninja@v6
       - name: Setup MSVC toolset (VS 2022)
         uses: TheMrMilchmann/setup-msvc-dev@v3
         if: matrix.os == 'windows-latest'