Add `LABEL_UPDATED` to `EventType` enum.

[BURG3R5]

In this issue, you'll add a new member to the EventType enum present in the file bot/models/github/event_type.py

The name of the member will be LABEL_UPDATED

The keyword for the member will be "lu"

The "docs" for the member will be "An Issue label was updated"

This issue is a part of a bigger issue (#6). Leave a comment if you have any doubts.

[shaked-h]

I would like to fix this issue. Can you please assign this to me?

[BURG3R5]

Hey @shaked-h, this issue is made specifically for Open Source Odyssey participants and will be assigned as the event progresses.

[shaked-h]

ok thank you.