💡(project) fix module docstring following black update

After a recent black update, some files were not correctly formatted. Fixing
them.

Author: wilbrdt

src/backend/marsha/bbb/management/commands/update_pending_classroom_sessions.py

@@ -1,5 +1,5 @@
 """For each pending classroom, get their meeting infos:
- update learning analytics, and end it if needed."""
+update learning analytics, and end it if needed."""
 
 from django.core.management import BaseCommand
 

src/backend/marsha/core/cache.py

@@ -1,9 +1,9 @@
 """
-    RedisCache with a fallback cache to prevent denial of service if Redis is down
-    Freely inspired by django-cache-fallback
+RedisCache with a fallback cache to prevent denial of service if Redis is down
+Freely inspired by django-cache-fallback
 
-    Credits:
-    - https://github.com/Kub-AT/django-cache-fallback/
+Credits:
+- https://github.com/Kub-AT/django-cache-fallback/
 """
 
 import logging

src/backend/marsha/core/lti/common.py

@@ -1,4 +1,4 @@
-""" Common classes and methods for LTi module"""
+"""Common classes and methods for LTi module"""
 
 from logging import getLogger
 from urllib.parse import urlencode