Bump seanmiddleditch/gha-setup-ninja from 4 to 6

Bumps [seanmiddleditch/gha-setup-ninja](https://github.com/seanmiddleditch/gha-setup-ninja) from 4 to 6.
- [Release notes](https://github.com/seanmiddleditch/gha-setup-ninja/releases)
- [Commits](seanmiddleditch/gha-setup-ninja@v4...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]>

Author: dependabot[bot]

.github/workflows/github_actions_build.yml

@@ -130,7 +130,7 @@ jobs:
       CXX: ${{ matrix.cxx-compiler }}
     steps:
       - uses: actions/checkout@master
-      - uses: seanmiddleditch/gha-setup-ninja@v4
+      - uses: seanmiddleditch/gha-setup-ninja@v6
         if: contains(matrix.generator, 'Ninja')
 
       - name: install boost
@@ -175,7 +175,7 @@ jobs:
       DEVELOPER_DIR: '/Applications/Xcode_${{ matrix.xcode-version }}.app/Contents/Developer'
     steps:
       - uses: actions/checkout@master
-      - uses: seanmiddleditch/gha-setup-ninja@v4
+      - uses: seanmiddleditch/gha-setup-ninja@v6
         if: contains(matrix.generator, 'Ninja')
 
       - name: install boost