fix(openapi): add required items field to iso_country_code array schema

Add items field to WidgetRequest.iso_country_code to comply with OpenAPI 3.0
specification requirement that array types must define their element types.

This change makes the schema technically valid without affecting documentation
display or user request construction, as the example array already demonstrates
the expected string values ["US", "CA"].

Author: Nicki Nixon

openapi/mx_platform_api.yml

@@ -7241,8 +7241,10 @@ components:
           description: |
             Only use this option if the `widget_type` is set to `connect_widget`. This indicates whether OAuth app2app behavior is enabled for institutions that support it. Defaults to `true`. When set to `false`, the widget will **not** direct the end user to the institution's mobile application. This setting is not persistent. This setting currently only affects Chase institutions.
         iso_country_code:
-          example: ["US", "CA"]
           type: array
+          items:
+            type: string
+          example: ["US", "CA"]
           description: |
             An array of strings that filters institutions in the widget by the specified country code. Acceptable codes include `US`, `CA`, and `MX` (Mexico).
         use_cases: