swift

d868e68c - [Concurrency] Allow conditionally conforming to `Sendable` when conformance is suppressed

[Concurrency] Allow conditionally conforming to `Sendable` when conformance is suppressed For consistency with invertible protocols using `~Sendable` should only prohibit use of unconditional extensions. For example: ```swift struct G<T>: ~Sendable {} ``` The following (unconditional) extension is rejected: ``` extension G: Sendable {} // error: cannot both conform to and suppress conformance to 'Sendable' ``` But conditional on `T` is accepted: ``` extension G: Sendable where T: Sendable {} // Ok! ```