This is non-standard AFAIK. Is there a reason this isn't using the normal MediaWiki qunit runner?
It seems like QUnit has nothing to do with the problem.
From the logs it seems like babel is trying to create a directory for its compilation cache but there is no access to the file system in the new docker based setup.
babel-register is used in development to run code with EcmaScript modules on node (for the tests).
Seems like the old setup had access to a file system and this one doesn't?