extbase classmap entry breaks composer create-project
when setting up a project composer based with
composer create-project typo3/cms cms ^8.7 -n
the command failes with
... Generating autoload files [RuntimeException] Could not scan for classes inside "typo3/sysext/extbase/Tests/Unit/Object/Container/Fixtures/" which does not appear to be a file nor a folder
This happens for the classmap entry in sysext:extbase/composer.jons line 41, that tries to load Test classes into autoload-dev autoloading. But thanks to Testclasses being excluded from the operation (git attributes I guess) the folder does not exist and the command fails.
One can work around that by adding --prefer-source to the create-project command, but that slows down the whole process a lot and ends up with all test classes in place.