Update specification of current maintainer?

[mekeor]

Currently, @Kha is mentioned as only maintainer of lean4-mode:

lean4-mode/lean4-mode.el

Line 10 in da7b63d

;; Maintainer: Sebastian Ullrich <sebasti@nullri.ch>

Is this statement up-to-date? Looking at the Git log, @bustercopley and @urkud have authored and committed most changes in the last 12 months. Please update the stated maintainer if needed.

If you are looking for a maintainer, I'd like to candidate.