???
Looks like a "bot gone wild" was let loose in here.

Well I'll be damned! (something my father used to say a lot - still not
sure what it means, though.)

Hmm, I just set up another attempt (new unpacking of the MW_1.30 tarball) and it worked this time. https://pastebin.com/z432ThAb

Sorry to keep adding to this, but looking a bit closer at the chameleon-skin dev's instructions (https://github.com/cmln/chameleon/blob/master/docs/installation-linux.md), it appears to be telling composer to add the skin to vendors/mediawiki, i.e.

Ok, after removing the vendor/mediawiki directory and rerunning composer update, it seems that command recreated the mediawiki directory, re-added at-ease, and also dropped bootstrap, chameleon-skin, and mediawiki-codesniffer into that same recreated 'vendor/mediawiki' directory.

Just some add'l info:
https://www.mediawiki.org/wiki/Skin:Chameleon/Installation
The above instructions are unhelpful for use with a RHEL/Centos 7 server:

Ok, then related to that thought, each time I have run composer, I also got the following warning:

Unfortunately, no joy yet