Add alex-semenyuk to twir-reviewers list

[alex-semenyuk]

As mentioned at rust-lang/this-week-in-rust#8644 I’d be glad to help

@nellshamrell

[github-actions]

Dry-run check results

[WARN  rust_team::sync] sync-team is running in dry mode, no changes will be applied.
[INFO  rust_team::sync] synchronizing crates-io
[INFO  rust_team::sync] synchronizing github
[INFO  rust_team::sync] 💻 Team Diffs:
    📝 Editing team 'rust-lang/twir-reviewers':
      Adding member 'alex-semenyuk' with member role

[apiraino]

As a reader of TwiR that's great to read, thanks @alex-semenyuk
From time to time AI-generated articles make it to get published in the newsletter. I would be happy if an additional "pair of eyes" could ensure the quality of the newsletter.

[nellshamrell]

@alex-semenyuk ty for letting me know! I will reach out to you, let's hold off on merging this pull request for the time being.

[jieyouxu]

(Marking as draft before team consensus.)