Return RubyString instead of Java String in Thread#status method

Author: andrykonchin

src/main/java/org/truffleruby/core/thread/ThreadNodes.java

@@ -582,7 +582,7 @@ Object status(RubyThread self) {
             }
 
             RubySymbol nameSymbol = threadStatusToRubySymbol(status, coreSymbols());
-            return nameSymbol.getString();
+            return createString(nameSymbol.tstring, nameSymbol.encoding);
         }
 
     }