[GR-3971] Add missing @Override in FastRTckTest.

com.oracle.truffle.r.test/src/com/oracle/truffle/r/test/tck/FastRTckTest.java

@@ -506,6 +506,7 @@ public class FastRTckTest extends TruffleTCK {
         return "valueWithSource";
     }
 
+    @Override
     protected String objectWithKeyInfoAttributes() {
         return "objectWithKeyInfoAttributes";
     }