[tests] Fix typing information in package:js tests

Makes this test consistent with the others in the "family"
which all use `String` as the return type.

Change-Id: Id50de839094f766f29170d4b42e922635e12683a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/423561
Commit-Queue: Nicholas Shahan <[email protected]>
Reviewed-by: Srujan Gaddam <[email protected]>

Author: nshahan

tests/lib/js/call_method_test.dart

@@ -28,13 +28,13 @@ import 'package:js/js.dart';
 import 'call_utils.dart';
 
 @JS('jsFunction')
-external int Function(String) jsFunctionAsFunction;
+external String Function(String) jsFunctionAsFunction;
 
 @JS('jsObject')
-external int Function(String) jsObjectAsFunction;
+external String Function(String) jsObjectAsFunction;
 
 @JS('jsClass')
-external int Function(String) jsClassAsFunction;
+external String Function(String) jsClassAsFunction;
 
 @JS('jsFunction')
 external Function jsFunctionAsFunctionInterface;
@@ -47,7 +47,7 @@ external Function jsClassAsFunctionInterface;
 
 @JS()
 class NamedClass {
-  external int call(String s);
+  external String call(String s);
 }
 
 @JS('jsFunction')
@@ -62,7 +62,7 @@ external NamedClass get jsClassAsNamedClass;
 @JS()
 @anonymous
 class SomeClass {
-  external int call(String s);
+  external String call(String s);
 }
 
 @JS('jsFunction')