Bump actions/setup-python from 6 to 6.3.0 (#32317)

Bumps [actions/setup-python](https://github.com/actions/setup-python) from 6 to 6.3.0.
- [Release notes](https://github.com/actions/setup-python/releases)
- [Commits](https://github.com/actions/setup-python/compare/v6...v6.3.0)

---
updated-dependencies:
- dependency-name: actions/setup-python
  dependency-version: 6.3.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

.github/workflows/ci.yml

@@ -26,7 +26,7 @@ jobs:
           bash tools/ci/install_build_deps.sh
           bash tools/ci/install_dreamchecker.sh
 
-      - uses: actions/setup-python@v6
+      - uses: actions/setup-python@v6.3.0
         with:
           python-version: '3.13'
           cache: 'pip'

.github/workflows/merge_upstream_master.yml

@@ -59,7 +59,7 @@ jobs:
           cache: 'yarn'
           cache-dependency-path: ./tgui/yarn.lock
 
-      - uses: actions/setup-python@v6
+      - uses: actions/setup-python@v6.3.0
         with:
           python-version: '3.13'
           cache: 'pip'