Update Sources/XCTest/Public/XCTestCase.TearDownBlocksState.swift

Co-authored-by: Stuart Montgomery <smontgomery@apple.com>

Author: Sean Olszewski

Sources/XCTest/Public/XCTestCase.TearDownBlocksState.swift

@@ -22,7 +22,7 @@ extension XCTestCase {
         private var blocks: [() throws -> Void] = []
 
         @available(macOS 12, *)
-        func append(_ block: @escaping () async throws -> Void) {
+        func append(_ block: @Sendable @escaping () async throws -> Void) {
             XCTWaiter.subsystemQueue.sync {
                 precondition(wasFinalized == false, "API violation -- attempting to add a teardown block after teardown blocks have been dequeued")
                 blocks.append {