[github-actions]: 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/publish-docs.yml

@@ -28,7 +28,7 @@ jobs:
       - uses: actions/checkout@v5
         with:
           fetch-depth: 0 # all history for all branches and tags
-      - uses: actions/setup-python@v5
+      - uses: actions/setup-python@v6
         with:
           python-version: 3.x
       - run: echo "cache_id=$(date --utc '+%V')" >> $GITHUB_ENV

.github/workflows/validate-docs.yml

@@ -18,7 +18,7 @@ jobs:
       - uses: actions/checkout@v5
         with:
           fetch-depth: 0 # all history for all branches and tags
-      - uses: actions/setup-python@v5
+      - uses: actions/setup-python@v6
         with:
           python-version: 3.x
       - run: echo "cache_id=$(date --utc '+%V')" >> $GITHUB_ENV