There is an updated pull request by Hoshpak against master on the void-packages repository

https://github.com/Hoshpak/void-packages mumble-1.3.0
https://github.com/void-linux/void-packages/pull/14245

mumble: update to 1.3.0.
staging to update when the stable release comes out and for interested people to build themselves.

A patch file from https://github.com/void-linux/void-packages/pull/14245.patch is attached