Bump actions/setup-python from 5 to 6 (#25)

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>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/cd-wheel.yml

@@ -138,7 +138,7 @@ jobs:
         brew install uv
 
     - id: setup-python
-      uses: actions/setup-python@v5
+      uses: actions/setup-python@v6
       with:
         python-version: 3
 

.github/workflows/ci.yml

@@ -39,7 +39,7 @@ jobs:
     if: ${{ github.event_name == 'pull_request' }}
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/setup-python@v5
+    - uses: actions/setup-python@v6
     - run: pipx run tox
 
   mpich-43: