Use social-media team for rust-artwork repo.

[m-ou-se]

See #2267 (comment) and #council > rust-lang/rust-artwork @ 💬

[github-actions]

Dry-run check results

[WARN  sync_team] sync-team is running in dry mode, no changes will be applied.
[INFO  sync_team] synchronizing crates-io
[INFO  sync_team] synchronizing github
[INFO  sync_team] 💻 Team Diffs:
    ➕ Creating team:
      Org: rust-lang
      Name: social-media
      Description: Managed by the rust-lang/team repository.
      Privacy: closed
      Members:
        m-ou-se: member
    💻 Repo Diffs:
    📝 Editing repo 'rust-lang/bors':
      Rulesets:
          Ruleset for main
            No changes
    📝 Editing repo 'rust-lang/rust-artwork':
      Permission Changes:
        Giving team 'social-media' write permission
        Removing team 'leadership-council''s write permission