Replace asyncio.iscoroutinefunction

[alexander-alderman-webb]

Around two years away, but eventually we will have to address the removal of asyncio.iscoroutinefunction. The inspect method was added in 3.5 but we should make sure there are no differences in behaviour across the versions we support. See https://docs.python.org/3/library/inspect.html

DeprecationWarning: 'asyncio.iscoroutinefunction' is deprecated and slated for removal in Python 3.16; use inspect.iscoroutinefunction() instead

[linear]

PY-1877