Roll rustfmt reviewers for in-tree rustfmt

[jieyouxu]

Noticed in #153229 (comment), where because src/tools/rustfmt has no corresponding [assign.owners] entry, it rolls one of the fallback reviewers (Mark and me) which is needless indirection, since if it rolls to Mark, Mark will have to reroll again.

This can also be

"/src/tools/rustfmt" = ["rustfmt", "rustfmt-contributors"]

which corresponds to https://github.com/orgs/rust-lang/teams/rustfmt and https://github.com/orgs/rust-lang/teams/rustfmt-contributors respectively. I will double-check with triagebot team if we can use review rotation toggles for rust-lang/rust in-tree rustfmt specifically.

Discussion: #t-rustfmt > review queue tracking for rust-lang/rust in-tree rustfmt

Unresolved question

• Do we want to start everyone off as off-rotation? Or on-rotation? I plan to start conservatively by preserving existing effective status, which is everyone off-rotation.

r? @ytmimi

[rustbot]

triagebot.toml has been modified, there may have been changes to the review queue.

cc @davidtwco, @wesleywiser