Update git submodules
- Update extensions/CiteThisPage from branch 'REL1_39' to 2f4bf4258af244898bdd4dd6cf6109a58d81721b
- Merge "build: Update MediaWiki requirement to 1.39.0" into REL1_39
- build: Update MediaWiki requirement to 1.39.0
Change-Id: I4b4ffbfdd4336fd16d2698c36866c5c5984605f4