Go through sentry 2.0 migration guide

[wookie184]

We should make sure we aren't using any of the methods deprecated in this major release, in the migration guide (https://docs.sentry.io/platforms/python/migration/1.x-to-2.x) push_scope is mentioned as being deprecated but we still use it here:

sir-lancebot/bot/exts/core/error_handler.py

Line 8 in 7bd936f

from sentry_sdk import push_scope

Originally posted by @wookie184 in #1519 (comment)

[jb3]

If it helps at all, the only change required for this is to literally swap push_scope for new_scope:

python-discord/bot@5b209b1 (#3047)

Our usages of push_scope are innocuous enough that the slight changes in behaviour are null for us.