core: workaround for crsf token in production for MarkdownInput

See https://docs.djangoproject.com/en/2.0/ref/csrf/#acquiring-the-token-if-csrf-use-sessions-is-true
Status Job ID Name Coverage
  Test
passed #1952
black

00:01:38

passed #1953
test

00:09:53

60.0%
canceled #1951
test

00:05:39