[SR-15296] CheckedContinuation should be sendable

[drewcrawford]

Previous ID	SR-15296
Radar	None
Original Reporter	@drewcrawford
Type	Bug

Environment

Apple Swift version 5.5 (swiftlang-1300.0.31.1 clang-1300.0.29.1)

Additional Detail from JIRA

Votes	0
Component/s	Standard Library
Labels	Bug
Assignee	None
Priority	Medium

md5: 7d70ca2abcdc2fe1656830c4369c66be

Issue Description:

Pretty sure this is just an oversight, as UnsafeContinuation is Sendable.

func assert(sendable: Sendable) {}
func example() {
 withCheckedContinuation { (continuation: CheckedContinuation<(),Never>) in
// Argument type 'CheckedContinuation<(), Never>' does not conform to expected type 'Sendable'
 assert(sendable: continuation) 
 }
}