Set up Python 3.12 for Swift formatting

The clang-format pre-commit job uses the repository's Python 3.12 hook environment, so install that interpreter before running pre-commit.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jketema

.github/workflows/swift.yml

@@ -58,6 +58,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v5
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
       - uses: pre-commit/action@646c83fcd040023954eafda54b4db0192ce70507
         name: Check that python code is properly formatted
         with: