Fix 80 column docstring

Author: WaVEV

django_mongodb_backend/query.py

@@ -125,9 +125,10 @@ def extra_where(self, compiler, connection):  # noqa: ARG001
 
 def join(self, compiler, connection, pushed_expression=None):
     """
-    Generate a MongoDB $lookup stage for a join. Optionally accepts a pushed_expression,
-    which is a filter expression involving fields from the joined collection, and
-    can be pushed into the lookup pipeline for optimization.
+    Generate a MongoDB $lookup stage for a join. Optionally accepts a
+    pushed_expression, which is a filter expression involving fields from the
+    joined collection, and can be pushed into the lookup pipeline for
+    optimization.
     """
 
     parent_template = "parent__field__"