Upgrade babel-eslint to @babel/eslint-parser

[karlhorky]

babel-eslint is now archived on GitHub, and eslint-plugin-unicorn version v32.0.0 will no longer support it:

Drop support for babel-eslint - You should migrate to @babel/eslint-parser

The eslint-config-upleveled package depends on eslint-config-react-app, which has not yet upgraded:

facebook/create-react-app#10761

Maybe we can still upgrade now, like in the changes of the PR above?

[karlhorky]

Doesn't seem to actually cause a problem, that we haven't switched from babel-eslint to @babel/eslint-parser ...

[karlhorky]

Done in f29dd66