test_templatetags: use inspect.isfunction in py3 (#38781)

In py2 inspect.ismethod returns bound or unbound method
whereas is py3 it return only bound method.

tests/test_templatetags.py

@@ -17,7 +17,7 @@
 import inspect
 
 from django.apps import apps
-from django.utils import translation
+from django.utils import six, translation
 
 from passerelle.base.templatetags.passerelle import render_body_schemas, render_json_schema
 
@@ -25,6 +25,7 @@ from passerelle.base.templatetags.passerelle import render_body_schemas, render_
 def test_render_body_schemas(db):
     # FIXME: db should be required but the way ProxyLogger is initialized force an access to the DB
     def collect_schemas():
+        predicate = inspect.isfunction if six.PY3 else inspect.ismethod
         for app in apps.get_app_configs():
             connector_model = None
             if not hasattr(app, 'get_connector_model'):
@@ -32,7 +33,7 @@ def test_render_body_schemas(db):
             connector_model = app.get_connector_model()
             if connector_model is None:
                 continue
-            for name, method in inspect.getmembers(connector_model, inspect.ismethod):
+            for name, method in inspect.getmembers(connector_model, predicate):
                 if not hasattr(method, 'endpoint_info'):
                     continue
                 if method.endpoint_info.post and method.endpoint_info.post.get('request_body', {}).get('schema'):