frozendict is invariant (python 3.15) #16668

# Mutable list is invariant
list1: list[int] = [10]
list2: list[int | None] = list1 # Error

# Immutable list (tuple) is covariant
tuple1: tuple[int, ...] = (10, )
tuple2: tuple[int | None, ...] = tuple1 # No Error

# Mutable dict is invariant
dict1: dict[str, int] = {"a": 10}
dict2: dict[str, int | None] = dict1 # Error 

# Immutable dict is also invariant????
fdict1: frozendict[str, int] = frozendict(a=10)
fdict2: frozendict[str, int | None] = fdict1 # Error
# But I think this should not be an error
# I think Key and Value should booth be covariant