highfives misses some PRs

[RalfJung]

Sometimes PRs get created without highfive reacting to them. Here is a recent example: rust-lang/rust#93194.

This is a problem because we are relying on highfive to notify us of changes in certain parts of the codebase, which is circumvented by these spurious outages.

[Xiretza]

Another example that actually seems to be related to the PR itself rather than a random outage: rust-lang/rust#100815 was missed, and when it was reopened as rust-lang/rust#100855 over a day later, it was missed again.