[py] Make `flake8` happy again

```
./test/test_mappers.py:126:43: E741 ambiguous variable name 'l'
./test/test_mappers.py:134:43: E741 ambiguous variable name 'l'
./cubicweb_jsonschema/mappers/base.py:56:26: E741 ambiguous variable name 'l'
```

cubicweb_jsonschema/mappers/base.py

 # copyright 2016-2021 LOGILAB S.A. (Paris, FRANCE), all rights reserved.
-# contact http://www.logilab.fr -- mailto:contact@logilab.fr
+# contact https://www.logilab.fr -- mailto:contact@logilab.fr
 #
 # This program is free software: you can redistribute it and/or modify it under
 # the terms of the GNU Lesser General Public License as published by the Free
@@ -12,7 +12,7 @@
 # details.
 #
 # You should have received a copy of the GNU Lesser General Public License
-# along with this program. If not, see <http://www.gnu.org/licenses/>.
+# along with this program. If not, see <https://www.gnu.org/licenses/>.
 """Base definitions for Yams to JSON Schema mappers."""
 
 import abc
@@ -52,8 +52,8 @@ def add_links(schema_and_definitions):
     def wrapper(self, schema_role=None):
         schema, defns = schema_and_definitions(self, schema_role=schema_role)
         if self.resource is not None and isinstance(schema, dict):
-            links = [l.description_object(self.resource)
-                     for l in self.links(schema_role=schema_role)]
+            links = [link.description_object(self.resource)
+                     for link in self.links(schema_role=schema_role)]
             # Sort links to get predictable results.
             links.sort(key=lambda l: (l['href'], l.get('rel')))
             if links:

test/test_mappers.py

 # copyright 2016-2021 LOGILAB S.A. (Paris, FRANCE), all rights reserved.
-# contact http://www.logilab.fr -- mailto:contact@logilab.fr
+# contact https://www.logilab.fr -- mailto:contact@logilab.fr
 #
 # This program is free software: you can redistribute it and/or modify it under
 # the terms of the GNU Lesser General Public License as published by the Free
@@ -12,7 +12,7 @@
 # details.
 #
 # You should have received a copy of the GNU Lesser General Public License
-# along with this program. If not, see <http://www.gnu.org/licenses/>.
+# along with this program. If not, see <https://www.gnu.org/licenses/>.
 
 import base64
 from datetime import datetime
@@ -123,7 +123,7 @@ class JSONSchemaMapperTC(CubicWebTC):
                 entity_mapper = self.vreg['mappers'].select(
                     'jsonschema.entity', cnx, etype='Book')
                 self.assertCountEqual(
-                    [type(l).__name__ for l in entity_mapper.links()],
+                    [type(link).__name__ for link in entity_mapper.links()],
                     ['EntityLink', 'TopicsLink', 'RelationLink'],
                 )
                 relation_mapper = self.vreg['mappers'].select(
@@ -131,7 +131,7 @@ class JSONSchemaMapperTC(CubicWebTC):
                     rtype='author', role='subject',
                 )
                 self.assertEqual(
-                    [type(l).__name__ for l in relation_mapper.links()],
+                    [type(link).__name__ for link in relation_mapper.links()],
                     ['RelationLink'],
                 )