shell: Fix broken mypy linting on asyncio.gather()

[jerry-skydio]

This used to work but somehow got broken by a mypy
version upgrade. Now the output of gather is treated
as a list and as a result type info by index is not
preserved. We have to manually declare the types by
asserting for it to be happy.

[jerry-skydio]

Reviews in this chain:
└#134 shell: Fix broken mypy linting on asyncio.gather()

[jerry-skydio]

#	head	base	diff	date	summary
0	e8daeef8	9bfa7fb9	diff	Dec 22 15:28 PM	1 file changed, 9 insertions(+), 2 deletions(-)