chore: track GitHub topic follow-up

[goanpeca]

Summary

• Removes the package keyword workaround because PyPI/project keywords do not update GitHub repository topics.
• Leaves issue [quality-keeper] Missing required topics (discoverability) #3 open for maintainer action in repo Settings.

Linked issue

Refs #3

Tests run

• git diff --check
• mamba run -n b2listen-issue-3 python -m compileall b2listen

Follow-up notes

• Current token has pull-only permission on backblaze-b2-samples/b2listen; GitHub topics update still returns 404.
• A maintainer with repository settings access must add b2-labs, backblaze-b2, and cloudstorage as GitHub repository topics before issue [quality-keeper] Missing required topics (discoverability) #3 can be closed.
• PR assignment and label application also require permissions this token does not have.