QL: Extend the tests slightly

Adds a test for when the call is to an outer, non-member predicate.

ql/test/queries/style/ImplicitThis/Good.qll

@@ -9,8 +9,13 @@ class Foo extends string {
 
   /* Okay because not a member predicate. */
   string getBaz() { result = Baz::baz() }
+
+  /* Okay because not a member predicate. */
+  string getOuterQuux() { result = getQuux() }
 }
 
+string getQuux() { result = "quux" }
+
 module Baz {
   string baz() { result = "baz" }
 }