Strengthen the type of SetterMethodCall

ql/lib/codeql/ruby/ast/Call.qll

@@ -123,7 +123,7 @@ class MethodCall extends Call, TMethodCall {
  * a[0] = 10
  * ```
  */
-class SetterMethodCall extends MethodCall {
+class SetterMethodCall extends MethodCall, TMethodCallSynth {
   SetterMethodCall() { this = TMethodCallSynth(_, _, _, true, _) }
 
   final override string getAPrimaryQlClass() { result = "SetterMethodCall" }

ql/lib/codeql/ruby/typetracking/TypeTrackerSpecific.qll

@@ -105,7 +105,6 @@ predicate basicStoreStep(Node nodeFrom, DataFlowPublic::LocalSourceNode nodeTo,
  */
 private string getSetterCallAttributeName(AST::SetterMethodCall call) {
   // TODO: this should be exposed in `SetterMethodCall`
-  not call instanceof AST::ElementReference and
   exists(string setterName |
     setterName = call.getMethodName() and result = setterName.prefix(setterName.length() - 1)
   )