STC LUB of List and Set is not Collection for Java 21

The new SequencedCollection interface introduced in Java 21 has altered the type inference results for mixed use of List and Set. Consider the following:

def x
x = [] as List
if (predicate()) {
  x = [] as Set
}
x

Under STC, the inferred type of the last occurrence of "x" has changed from Collection to Object.