This test creates an object then checks a weak reference to that object on a background thread. It was doing this check after 10ms, and any small hiccup could potentially delay the object's destruction enough to spuriously fail.
Rearrange the test to check the weak reference in a loop for several seconds before giving up. This makes it very fast on success (it's done the moment it sees nil) while being robust against up to several seconds of delay in destroying the object if that happens.
rdar://149868181
Unfortunately we've encountered another source
breaking case here:
```
class C {
func method() {}
func foo() {
Task { [weak self] in
Task {
method()
}
}
}
}
```
In 5.10 we'd only do the unqualified lookup for
`self` when directly in a `weak self` closure,
but with the implicit self rework, we'd start
using the `weak self` here, leading to a
type-checker error.
At this point, adding more edge cases to the
existing logic is going to make things much more
complicated. Instead, reinstate the 5.10 implicit
self lookup behavior and diagnostic logic,
switching over to the new logic only under Swift 6
mode.
rdar://129475277
