Add REQUIRES: objc_interop to test

Author: aschwaighofer

test/IRGen/metadata_lookup_generic_objc.sil

@@ -2,6 +2,8 @@
 // RUN: %build-irgen-test-overlays
 // RUN: %target-swift-frontend(mock-sdk: -sdk %S/Inputs -I %t) %s -emit-ir | %FileCheck %s
 
+// REQUIRES: objc_interop
+
 import Builtin
 import Swift
 import gizmo