fix: fix syntax for Deprecationwarning (#942)

Author: busunkim96

gapic/ads-templates/%namespace/%name/%version/%sub/services/%service/client.py.j2

@@ -339,7 +339,7 @@ class {{ service.client_name }}(metaclass={{ service.client_name }}Meta):
         """
         {% if method.is_deprecated %}
         warnings.warn("{{ service.client_name }}.{{ method.name|snake_case }} is deprecated",
-            warnings.DeprecationWarning)
+            DeprecationWarning)
 
         {% endif %}
         {% if not method.client_streaming %}

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

@@ -201,7 +201,7 @@ class {{ service.async_client_name }}:
         """
         {% if method.is_deprecated %}
         warnings.warn("{{ service.async_client_name }}.{{ method.name|snake_case }} is deprecated",
-            warnings.DeprecationWarning)
+            DeprecationWarning)
 
         {% endif %}
         {% if not method.client_streaming %}

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

@@ -364,7 +364,7 @@ class {{ service.client_name }}(metaclass={{ service.client_name }}Meta):
         """
         {% if method.is_deprecated %}
         warnings.warn("{{ service.client_name }}.{{ method.name|snake_case }} is deprecated",
-            warnings.DeprecationWarning)
+            DeprecationWarning)
 
         {% endif %}
         {% if not method.client_streaming %}