update template (#1563)

Author: skarimo

.generator/src/generator/templates/api_client.j2

@@ -132,7 +132,7 @@ class ApiClient:
 
         if return_http_data_only:
             return return_data
-        return (return_data, response.status, response.headers.copy())
+        return (return_data, response.status, dict(response.headers))
 
     def parameters_to_multipart(self, params):
         """Get parameters as list of tuples, formatting as json if value is dict.

.generator/src/generator/templates/exceptions.j2

@@ -94,7 +94,7 @@ class ApiException(OpenApiException):
                 self.body = json.loads(http_resp.data)
             except Exception:
                 self.body = http_resp.data.decode("utf-8")
-            self.headers = http_resp.headers.copy()
+            self.headers = dict(http_resp.headers)
         else:
             self.status = status
             self.reason = reason