Bump actions/setup-python from 5 to 6

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

---
updated-dependencies:
- dependency-name: actions/setup-python
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/build-toolchain.yml

@@ -161,7 +161,7 @@ jobs:
         run: rm -f /usr/local/lib/pkgconfig/libzstd.pc /usr/local/include/zstd.h
 
       # release-5.9 requires 3.11 or lower Python
-      - uses: actions/setup-python@v5
+      - uses: actions/setup-python@v6
         if: ${{ startsWith(matrix.build_os, 'macos-') && (matrix.scheme == 'release-5.9' || matrix.scheme == 'release-5.10') && (matrix.agent_query == 'macos-13' || matrix.agent_query == 'macos-14') }}
         with:
           python-version: '3.11'