Use 'run' function instead of 'synchronized' in KT-51036 test

It should be enough to reproduce the issue and makes the test runnable on all backends

compiler/testData/codegen/box/unit/kt51036.kt

@@ -1,8 +1,4 @@
 // WITH_STDLIB
-// IGNORE_BACKEND: WASM
-//  ^ Unresolved reference: synchronized
-// IGNORE_BACKEND: NATIVE
-//  ^ Unresolved reference: synchronized
 
 fun box(): String {
     A().close()
@@ -12,6 +8,5 @@ fun box(): String {
 class A {
     companion object;
     operator fun String.invoke() = Unit
-    @Suppress("DEPRECATION_ERROR")
-    fun close() = synchronized(this) { "abc" }()
+    fun close() = kotlin.run { "abc" }()
 }