when asking a team for review, don't assign to people that are on vacation/off

[matthiaskrgr]

could avoid bouncing from person to person as seen here rust-lang/rust#149800 (comment)

[Kobzol]

Huh, that should already happen, so this seems like a bug. I'll take a look, thanks.

[Kobzol]

Hmm, very weird. The code should filter these people out... I'd need a fresher repro to take a look at the logs.