Move fallthrough one line up

Author: shabalind

stdlib/public/runtime/DynamicCast.cpp

@@ -862,8 +862,8 @@ tryCastToString(
       destFailureType, srcFailureType,
       takeOnSuccess, mayDeferChecks);
 #endif
-  }
     SWIFT_FALLTHROUGH;
+  }
   default:
     return DynamicCastResult::Failure;
   }