[Concurrency] Unskip isolated-conformance runtime test on WebAssembly

Author: kateinoigakukun

test/Concurrency/Runtime/isolated_conformance.swift

@@ -5,12 +5,6 @@
 // REQUIRES: concurrency_runtime
 // UNSUPPORTED: back_deployment_runtime
 
-// FIXME: WebAssembly doesn't currently have a good way to install the
-// "isCurrentGlobalActor" hook on which this checking depends. Disable
-// the test for the moment.
-// UNSUPPORTED: wasm
-// UNSUPPORTED: CPU=wasm32
-
 protocol P {
   func f()
 }
@@ -207,6 +201,10 @@ await Task.detached { @SomeGlobalActor in
 // CHECK: Testing a separate task off the main actor
 print("Testing a separate task off the main actor")
 await Task.detached {
+  // Skip tests on platforms that use the same executor for the main
+  // actor and the global concurrent executor.
+  guard Task.defaultExecutor !== MainActor.executor else { return }
+
   if #available(SwiftStdlib 6.2, *) {
     precondition(!tryCastToP(mc))
     precondition(!tryCastToP(wrappedMC))