ci(deps): 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/ci-act.yml

@@ -32,7 +32,7 @@ jobs:
 
     - name: Set up Python (GitHub Actions only)
       if: ${{ !env.ACT }}
-      uses: actions/setup-python@v5
+      uses: actions/setup-python@v6
       with:
         python-version: ${{ env.PYTHON_VERSION }}
 
@@ -98,7 +98,7 @@ jobs:
 
     # Act-compatible Python and uv setup
     - name: Set up Python
-      uses: actions/setup-python@v5
+      uses: actions/setup-python@v6
       with:
         python-version: ${{ matrix.python-version }}
 
@@ -135,7 +135,7 @@ jobs:
 
     # Act-compatible Python and uv setup
     - name: Set up Python
-      uses: actions/setup-python@v5
+      uses: actions/setup-python@v6
       with:
         python-version: ${{ env.PYTHON_VERSION }}
 
@@ -183,7 +183,7 @@ jobs:
 
     # Act-compatible Python and uv setup
     - name: Set up Python
-      uses: actions/setup-python@v5
+      uses: actions/setup-python@v6
       with:
         python-version: ${{ env.PYTHON_VERSION }}