This updates the Joomla DI package to 1.3.0 to address a bug in resolving aliases in the package. As the package is unused in the CMS at present, there is no simple way to test this PR.
Because of running composer update --no-dev joomla/di, it appears the base ClassLoader class has also been updated. This aspect is testable. If you are able to log into the admin, get to an edit screen, and save the item I'd call that a success as that should trigger Composer's autoloader for several objects.