Upgrade to Git v2.28.0.rc1
Git v2.28.0.rc1 has been released. As the v2.28.0 release series is the first to contain support for the reference-transaction hook which is currently a focus for Gitaly, this commit adds the release candidate version so we can test the hook as part of Gitaly's CI.
Part of: gitaly#2959 (closed)
Edited by Zeger-Jan van de Weg