pylint: Pin pylint version to avoid error

Letting pylint freely upgrade tends to result in surprise errors, so pin
the version. There's a warning we'll probably need to disable later,
though maybe pylint will get smarter instead.

setup.py

@@ -17,7 +17,7 @@
         'scripts': ['flup'], # index.fcgi needs flup
         'mysql': ['mysqlclient'],
         'dev': [
-            'pylint', 'pylint-django',  # lint
+            'pylint<3.2.0', 'pylint-django',  # lint
             'mypy', 'django-stubs',     # type checking
         ],
         'doc': ['sphinx'],

squaresdb/gate/views.py

@@ -401,6 +401,7 @@ def signin_api(request):
         return exc.response
 
     data['payment'] = payment.pk if paid else 0
+    # pylint exception possibly-used-before-assignment needed starting in 3.2.0
     data['attendee'] = attendee.pk if present else 0
 
     return JsonResponse(data=data, status=HTTPStatus.CREATED)