add concurrency avail guard to AsyncSequenceOfOne (#1671)

rnro · web-flow · commit ac2749584ce0 · 2023-10-10T13:51:35.000+01:00
Motivation:

Building fails with
```
error: concurrency is only available in macOS 10.15.0 or newer
```

Modifications:

Add an availability guard to `AsyncSequenceOfOne`

Result:

Code will build.
diff --git a/Sources/GRPCCore/Stream/AsyncSequenceOfOne.swift b/Sources/GRPCCore/Stream/AsyncSequenceOfOne.swift
@@ -30,6 +30,7 @@ extension RPCAsyncSequence {
 }
 
 /// An `AsyncSequence` of a single value.
+@available(macOS 10.15, iOS 13.0, tvOS 13, watchOS 6, *)
 private struct AsyncSequenceOfOne<Element: Sendable, Failure: Error>: AsyncSequence {
   private let result: Result<Element, Failure>
 

Original file line number	Diff line number	Diff line change
`@@ -30,6 +30,7 @@ extension RPCAsyncSequence {`
`30`	`30`	`}`
`31`	`31`
`32`	`32`	/// An `AsyncSequence` of a single value.
	`33`	`+@available(macOS 10.15, iOS 13.0, tvOS 13, watchOS 6, *)`
`33`	`34`	`private struct AsyncSequenceOfOne<Element: Sendable, Failure: Error>: AsyncSequence {`
`34`	`35`	`private let result: Result<Element, Failure>`
`35`	`36`