Bump d.py version to 2.4.0

[Jackenmen]

Description of the changes

Nothing major really:

• added exports of new things in app_commands namespace
• updated bot owner check only to consider Team Owner, Admins, and Developers when --team-members-are-owners flag is used
  • also added an alternative name for the flag that more accurately describes it - --team-developers-are-owners
• added [p]set bot banner command using the newly added API (fixes #6321)
• updated Filter cog to consider poll contents (and attachment's alt text) when checking for hits

Things I ignored:

• switch [p]massban to use the new mass ban API - this requires more effort than I think it is worth but it's worth considering in the future

Have the changes in this PR been tested?

No

[Jackenmen]

I'll bump the rest of the bumps in a separate PR closer to the release.