[Coroutines] Fix a few failing tests

Summary:
https://reviews.llvm.org/D82029 introduced the non-throw check for final_suspend(). There are a few tests I missed in that patch.
Fixing them here.

Reviewers: #libc, lewissbaker, modocache, ldionne

Reviewed By: #libc, ldionne

Subscribers: dexonsmith, modocache, libcxx-commits

Tags: #libc

Differential Revision: https://reviews.llvm.org/D82338