[Snip]
Yes, those are just warnings. All of them but the penultimate one has been fixed in MediaWiki 1.35.0 (just released), but are nothing to worry about unless you're maintaining the libraries that MediaWiki itself uses (e.g., me). For the PHPUnit ones in particular, it's unhelpful because the removed library is required for our current version of the tool, but replaced for the later ones that we're not using yet as we're still running instances on PHP 7.2.