apps/documents: fix typo in document template tag to make the reload …

[goapunk]

…on submit work again

see https://github.com/liqd/adhocracy-plus/issues/2590

Describe your changes Briefly explain what you did and provide context for a clearer understanding.

Tasks

• [ ] PR name contains story or task reference
• [ ] Steps to recreate and test the changes
• [ ] Documentation (docs and inline)
• [ ] Tests (including n+1 and django_assert_num_queries where applicable)
• [x] Changelog