build(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
...

Originally-authored-by: dependabot[bot] <support@github.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

.github/workflows/main.yml

@@ -259,7 +259,7 @@ jobs:
       cancel-in-progress: ${{ needs.ci-config.outputs.skip_concurrent == 'yes' }}
     steps:
     - uses: actions/checkout@v5
-    - uses: actions/setup-python@v5
+    - uses: actions/setup-python@v6
     - name: Set up dependencies
       shell: pwsh
       run: pip install meson ninja
@@ -287,7 +287,7 @@ jobs:
       cancel-in-progress: ${{ needs.ci-config.outputs.skip_concurrent == 'yes' }}
     steps:
     - uses: actions/checkout@v5
-    - uses: actions/setup-python@v5
+    - uses: actions/setup-python@v6
     - name: Set up dependencies
       shell: pwsh
       run: pip install meson ninja