Suppress Swift 6 concurrency warning when using XCTWaiter and XCTestExpectation.

This change annotates the `fulfillment(of:)` overloads so that they won't
trigger Swift 6 diagnostics. This is a late-breaking change that has started to
[affect](https://forums.swift.org/t/swift-5-10-concurrency-and-xctest/69929)
developers using strict concurrency checking with Swift 5.10.

Resolves rdar://124966292.

Author: grynspan

Sources/XCTest/Public/Asynchronous/XCTWaiter.swift

@@ -277,7 +277,7 @@ open class XCTWaiter {
     ///   swift-corelibs-xctest and Apple XCTest, it is not recommended to pass
     ///   explicit values for `file` and `line`.
     @available(macOS 12.0, *)
-    @discardableResult
+    @discardableResult @_unsafeInheritExecutor
     open func fulfillment(of expectations: [XCTestExpectation], timeout: TimeInterval, enforceOrder: Bool = false, file: StaticString = #file, line: Int = #line) async -> Result {
         return await withCheckedContinuation { continuation in
             // This function operates by blocking a background thread instead of one owned by libdispatch or by the
@@ -327,7 +327,7 @@ open class XCTWaiter {
     ///   expectations are not fulfilled before the given timeout. Default is the line
     ///   number of the call to this method in the calling file. It is rare to
     ///   provide this parameter when calling this method.
-    @available(macOS 12.0, *)
+    @available(macOS 12.0, *) @_unsafeInheritExecutor
     open class func fulfillment(of expectations: [XCTestExpectation], timeout: TimeInterval, enforceOrder: Bool = false, file: StaticString = #file, line: Int = #line) async -> Result {
         return await XCTWaiter().fulfillment(of: expectations, timeout: timeout, enforceOrder: enforceOrder, file: file, line: line)
     }

Sources/XCTest/Public/Asynchronous/XCTestCase+Asynchronous.swift

@@ -110,7 +110,7 @@ public extension XCTestCase {
     ///   provide this parameter when calling this method.
     ///
     /// - SeeAlso: XCTWaiter
-    @available(macOS 12.0, *)
+    @available(macOS 12.0, *) @_unsafeInheritExecutor
     func fulfillment(of expectations: [XCTestExpectation], timeout: TimeInterval, enforceOrder: Bool = false, file: StaticString = #file, line: Int = #line) async {
         let waiter = XCTWaiter(delegate: self)
         await waiter.fulfillment(of: expectations, timeout: timeout, enforceOrder: enforceOrder, file: file, line: line)