Replace hashCode usages in tests where it was supposed to fail on nullable receiver

Related to #KT-25039

jps-plugin/testData/incremental/classHierarchyAffected/enumMemberChanged/Enum.kt

@@ -4,4 +4,6 @@ enum class Enum(x: String) {
 
     val becameNullable: Any = x
     val unchanged: Any = x
-}
+}
+
+fun Any.string() = this as String

jps-plugin/testData/incremental/classHierarchyAffected/enumMemberChanged/Enum.kt.new.1

@@ -4,4 +4,6 @@ enum class Enum(x: String) {
 
     val becameNullable: Any? = x
     val unchanged: Any = x
-}
+}
+
+fun Any.string() = this as String

jps-plugin/testData/incremental/classHierarchyAffected/enumMemberChanged/useBecameNullable.kt

@@ -1,5 +1,5 @@
 import Enum.*
 
 fun useBecameNullable(e: Enum) {
-    println(e.becameNullable.hashCode())
+    println(e.becameNullable.string())
 }

jps-plugin/testData/incremental/classHierarchyAffected/enumMemberChanged/useBecameNullable.kt.new.2

@@ -1,5 +1,5 @@
 import Enum.*
 
 fun useBecameNullable(e: Enum) {
-    println(e.becameNullable?.hashCode())
+    println(e.becameNullable?.string())
 }

jps-plugin/testData/incremental/classHierarchyAffected/enumMemberChanged/useUnchanged.kt

@@ -1,5 +1,5 @@
 import Enum.*
 
 fun useUnchanged(e: Enum) {
-    println(e.unchanged.hashCode())
+    println(e.unchanged.string())
 }