runtime(python): Also sync syntax at 'async def'

runtime(python): Also sync syntax at 'async def'

A file containing only async functions (`async def func()`) wouldn't
previously match the pythonSync pattern.

Also, this pattern only matches at the beginning of the line, so it
won't ever match method definitions (which are indented within class
scopes). Update the comment accordingly.

closes: #17963

Signed-off-by: Jon Parise <jon@indelible.org>
Signed-off-by: Zvezdan Petkovic <zpetkovic@acm.org>
Signed-off-by: Christian Brabandt <cb@256bit.org>