[feature request] Replace `@<name>` in PR description with only `<name>`

[tesuji]

Otherwise the reviewer will be pinged when the PR is rollupped or bor try,
or even after the PR merged, the reviewer will be pinged by forks pulling the changes on github.

Originally posted by @lzutao in rust-lang/rust#76161 (comment)

cc @matklad as he is also asking for this.