fix: syntax fix for required_fields struct in rest transport

gapic/templates/%namespace/%name_%version/%sub/services/%service/transports/rest.py.j2

@@ -170,7 +170,7 @@ class {{service.name}}RestTransport({{service.name}}Transport):
     {% if method.input.required_fields %}
     __{{ method.name | snake_case }}_required_fields_default_values =  {
     {% for req_field in method.input.required_fields if req_field.is_primitive %}
-        "{{ req_field.name | camel_case }}" : {% if req_field.field_pb.default_value is string %}"{{req_field.field_pb.default_value }}"{% else %}{{ req_field.field_pb.default_value }}{% endif %}{# default is str #}
+        "{{ req_field.name | camel_case }}" : {% if req_field.field_pb.default_value is string %}"{{req_field.field_pb.default_value }}"{% else %}{{ req_field.field_pb.default_value }}{% endif %},{# default is str #}
     {% endfor %}
     }
 

gapic/templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2

@@ -7,7 +7,9 @@ import mock
 
 import grpc
 from grpc.experimental import aio
+{% if "rest" in opts.transport %}
 import json
+{% endif %}
 import math
 import pytest
 from proto.marshal.rules.dates import DurationRule, TimestampRule