Report warning about implicitly inferred nothing only for return position

^KT-31535 Fixed

compiler/testData/diagnostics/tests/j+k/flexibleNothing.kt

@@ -12,7 +12,7 @@ public class TestClass {
 fun run() {
     val testClass = TestClass()
     // inferred as `set<Nothing>()`, return type is Nothing!
-    testClass.<!OI;IMPLICIT_NOTHING_AS_TYPE_PARAMETER!>set<!>("test", null)
+    testClass.set("test", null)
 
     // Should not be unreachable
     run()