Make test_await more robust

tests/test_dunder.rs

@@ -612,7 +612,9 @@ async def main():
 # but we see still errors on Github actions...
 if sys.platform == "win32" and sys.version_info >= (3, 8, 0):
     asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())
-loop = asyncio.get_event_loop()
+# get_event_loop can cause error: see https://github.com/PyO3/pyo3/pull/961#issuecomment-645238579
+loop = asyncio.new_event_loop()
+asyncio.set_event_loop(loop)
 assert loop.run_until_complete(main()) is None
 loop.close()
 "#