https://github.com/civicrm/civicrm-core/blob/1ff2405992ac45df88425ff400a2c37f6056d938/install/civicrm.php#L134
It's now under vendor.
This would affect 5.30 too.
added regression label
PR https://github.com/civicrm/civicrm-core/pull/18473
PR has been merged
closed
changed milestone to %5.30.0
mentioned in commit b6d5ef33