This means that:
1. In test cases where minimal is the default (swift 5 without
-warn-concurrency), I added RUN lines for targeted, complete, and complete +
sns.
2. In test cases where complete is the default (swift 6, -warn-concurrency,
specified complete with -strict-concurrency), I added a send non-sendable run
line.
In each of these cases, I added additional expected-* lines as appropriate so
the tests can compile in each mode successfully.
The fix-it was being a little too eager to label function decls async.
Computed properties, or AccessorDecls are function declarations, but
they don't have parentheses, so trying to add `async` to them causes
crashing. Furthermore, they can't be async at all, so suggesting that we
make them async is just wrong. We shouldn't give folks a glimmer of hope
where there is none to be had.
