Don't check units during initialization

[ctessum]

...because initialization problems don't correctly handle units and units have already been checked during system initialization.

Checklist

• [X] Appropriate tests were added
• [X] Any code changes were done in a way that does not break public API
• [X] All documentation related to code changes were updated
• [X] The new code follows the contributor guidelines, in particular the SciML Style Guide and COLPRAC.
• [X] Any new documentation only uses public API

Additional context

Fixes #3086