Rather than assuming, I checked the Bridgy source, which uses Granary for this, and verified that Granary does have an explicitly enumerated list for the reacji that GitHub allows.
Submitted https://github.com/snarfed/granary/pull/186 to add Granary support for the new 🚀👀 reacji in GitHub, and thus in Bridgy.
Please commit and deploy that pull request first before this one.
Alter reality before updating the documentation about reality. Thanks!