Upgrade to sorl-thumbnail==12.4.1

Note: thumbnail.0001_initial migration was not in my django_migrataion
table, so after this upgrade I was prompted to apply the migration, which
then errored out because the thumbnail_kvstore table already exists.

Probably related to the issue here:
jazzband/sorl-thumbnail#458

To fix, I just manually added a row to django_migrations to indicate
that this migration was already applied.

requirements.txt

@@ -18,5 +18,5 @@ requests==2.27.1
 requests-oauthlib==1.2.0
 requests-toolbelt==0.9.1
 six==1.12.0
-sorl-thumbnail==12.3
+sorl-thumbnail==12.4.1
 urllib3==1.26.5