4.1.0

• Adapted to API changes made in Trio v0.23:
  • Call trio.to_thread.run_sync() using the abandon_on_cancel keyword argument instead of cancellable
  • Removed a checkpoint when exiting a task group
  • Renamed the cancellable argument in anyio.to_thread.run_sync() to abandon_on_cancel (and deprecated the old parameter name)
  • Bumped minimum version of Trio to v0.23
• Added support for voluntary thread cancellation via anyio.from_thread.check_cancelled()
• Bumped minimum version of trio to v0.23
• Exposed the ResourceGuard class in the public API (#627)
• Fixed RuntimeError: Runner is closed when running higher-scoped async generator fixtures in some cases (#619)
• Fixed discrepancy between asyncio and trio where reraising a cancellation exception in an except* block would incorrectly bubble out of its cancel scope (#634)