Bump md-addins to new head of monodevelop-5.1.1-branch

Includes 2 commits (one merge commit):
https://github.com/xamarin/md-addins/compare/5b679dd8620d608b36a1aee80c3a2bcc05377f43...016eae19105eaae2c441f8b8c9f43678eb048288

Fixes #20765