QL: Fix up getASuperType

I'm not sure if it's correct to include also the `instanceof`s, but we
can always fix this later.

Author: tausbn

ql/src/codeql_ql/ast/Ast.qll

@@ -665,7 +665,7 @@ class Class extends TClass, TypeDeclaration, ModuleDeclaration {
   /**
    * Gets a super-type referenced in the `extends` part of the class declaration.
    */
-  TypeExpr getASuperType() { toGenerated(result) = cls.getChild(_) }
+  TypeExpr getASuperType() { toGenerated(result) in [cls.getExtends(_), cls.getInstanceof(_)] }
 
   /** Gets the type that this class is defined to be an alias of. */
   TypeExpr getAliasType() {