Make testImplicitCancellationOnEdit more robust

Instead of adding an arbitrary `Task.sleep` that should give us enough time to send the `textDocument/didChange` notification, use a semaphore to coordinate the messages.

Author: ahoppen

Tests/SourceKitLSPTests/SemanticTokensTests.swift

@@ -894,11 +894,11 @@ final class SemanticTokensTests: XCTestCase {
   }
 
   func testImplicitCancellationOnEdit() async throws {
+    let didSendDocumentChange = WrappedSemaphore(name: "Did send document change")
     let testClient = try await TestSourceKitLSPClient(
       hooks: Hooks(preHandleRequest: { request in
         if request is DocumentSemanticTokensRequest {
-          // Sleep long enough for the edit to be handled
-          try? await Task.sleep(for: .seconds(10))
+          didSendDocumentChange.waitOrXCTFail()
         }
       })
     )
@@ -916,6 +916,7 @@ final class SemanticTokensTests: XCTestCase {
         contentChanges: [TextDocumentContentChangeEvent(range: Range(positions["1️⃣"]), text: "let x = 1")]
       )
     )
+    didSendDocumentChange.signal()
     try await fulfillmentOfOrThrow([receivedSemanticTokensResponse])
   }