Do not show error trace to the user

[bkchr]

The bot currently is posting the full error context into a github comment. As an example see here: paritytech/substrate#12723 (comment)

It should only post:

@bkchr ERROR: Error: Contributor did not properly post their account address.

Make sure the pull request description has: "{network} address: {address}".

[bkchr]

@parutger was the fix for this issue already deployed?

Because I just got it again: paritytech/substrate#12833 (comment)

[parutger]

@bkchr Thanks for the feedback, It wasn't deployed to production yet.
It is deployed now!