I looked into the source and probably it’s linked to this comment (not 100% validated):
// Inputs flagged as pass-by-reference will also be flagged as 'const' here to conform to the expected native C++
// declaration of 'const Type&' for input reference parameters on functions with no outputs (i.e. events). Array
// types are also flagged as 'const' here since they will always be implicitly passed by reference, regardless of
// the checkbox setting. See UEditablePinBase::PostLoad() for more details.