chore(gh-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] <support@github.com>

Author: dependabot[bot]

.github/workflows/ci-cd-mkdocs.yml

@@ -21,7 +21,7 @@
       steps:
         - uses: actions/checkout@v5
         - name: Install Python
-          uses: actions/setup-python@v5
+          uses: actions/setup-python@v6
           with:
             python-version: '3.11'
         - name: Install package with optional dependency 'doc'

.github/workflows/ci-cd.yml

@@ -21,7 +21,7 @@
           - name: Checkout
             uses: actions/checkout@v5
           - name: Set up Python version
-            uses: actions/setup-python@v5
+            uses: actions/setup-python@v6
             with:
               python-version: |
                 3.9
@@ -54,7 +54,7 @@
           - name: Checkout
             uses: actions/checkout@v5
           - name: Set up Python version
-            uses: actions/setup-python@v5
+            uses: actions/setup-python@v6
             with:
               python-version: '3.13'
           - name: Build package