synapse fails to start if wrong version of isort is installed

[richvdh]

This seems to be a recent regression.

Why does having the wrong version of isort installed prevent synapse from starting? Synapse doesn't use isort at runtime, so surely this makes no sense?

(env3)rav@fred:~/work/synapse (develop *$%=)$ python -m synapse.app.homeserver
ERROR:root:Needed optional isort==5.0.3, got isort==5.0.5
Missing Requirements: 'isort==5.0.3'
To install run:
    pip install --upgrade --force 'isort==5.0.3'

[clokep]

Regression from #8330, most likely.

[ShadowJonathan]

My apologies, I didn't know it would have this knock-on effect