[SR-14560] Add async alternative creates method that doesn't compile if Error parameter is generic

[ahoppen]

Previous ID	SR-14560
Radar	rdar://problem/77399843
Original Reporter	@ahoppen
Type	Bug

Additional Detail from JIRA

Votes	0
Component/s	Source Tooling
Labels	Bug
Assignee	None
Priority	Medium

md5: d1424c0305e9784a9152df0805d688bc

Issue Description:

Adding an async alternative to this method

func genericError<E>(completion: (String?, E?) -> Void) where E: Error { }

creates

func genericError<E>() async throws -> String where E: Error { }

which doesn’t compile because E is not used in the async method’s function signature.

[ahoppen]

@swift-ci create