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 underlying problem was that the ActorIsolationChecker was not properly
recording the mutation environment in which a lookup through an existential was
happening. That's because the AST looks like this:
```
(inout_expr ...
(open_existential_expr ...
(opaque_value_expr ...
(declref_expr ...
(member_ref_expr ...
(opaque_value_expr ...
```
and the walker creates a link from the `open_existential_expr` to the `inout_expr`,
but that kind of expression is not checked for its usage environment. Instead, we
need to look through that OpenExistentialExpr recursively so that a link from
its sub-expression, the `member_ref_expr`, to the `inout_expr` is formed instead.
The side-effect of that missing link causing the bug is that the `usageEnv` of
that `member_ref_expr` appears to be empty when we don't have the link. A missing
link is assumed to mean that it's not in a mutating environment, and thus the
usage is treated as a read.
This is why in #59573 / rdar://95509917 we are seeing the compiler report that an
`await` is needed around the assignment expr. The checker thinks it's a read, but
it's actually a mutation, because the member ref is happening in an `inout` expr.
Resolves rdar://95509917
Resolves#59573
