Additional test coverage for async rendering of native type templates

[jayaddison]

• fixes #1806

Checklist:

• [x] Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• [ ] ~~Add or update relevant docs, in the docs folder and in code.~~
• [x] Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• [ ] ~~Add .. versionchanged:: entries in any relevant code docs.~~
• [x] Run pre-commit hooks and fix any issues.
• [x] Run pytest ~~and tox~~, no tests failed.
  • PYTHONPATH=src pytest tests/test_nativetypes.py