Suppress warning building WASI

Author: grynspan

Sources/Testing/Test+Cancellation.swift

@@ -152,7 +152,7 @@ private func _cancel<T>(_ cancellableValue: T?, for testAndTestCase: (Test?, Tes
 #if !SWT_NO_EXIT_TESTS
     inExitTest = (ExitTest.current != nil)
 #endif
-    if inExitTest {
+    if Bool(inExitTest) {
       // This code is running in an exit test. We don't have a "current test" or
       // "current test case" in the child process, so we'll let the parent
       // process sort that out.