Update git submodules
- Update extensions/CategoryTree from branch 'REL1_39' to 3ab15a610feed9e770af51b379aa3bdcb0920c85
- build: Update MediaWiki requirement to 1.39.0
Change-Id: I72c59fdabb7137ca35f71ea48195ed56f998f237
- build: Update MediaWiki requirement to 1.39.0