Problem updating babel dependency

[bmispelon]

Looks like the migration check breaks when updating babel: #1593

I haven't had time to investigate, but it seems that upgrading babel triggers some changes in some models in the foundation app (from the CI failure in the PR linked above):

 Migrations for 'foundation':
  foundation/migrations/0005_alter_approvedgrant_amount_currency_and_more.py
    - Alter field amount_currency on approvedgrant
    - Alter field treasurer_balance_currency on meeting

We have a check that triggers a failure when such changes happen, which is why the PR has a red mark.

I don't have time to look at it right now, so if anyone wants to dig into the issue, they are most welcome.