[Issue 21807] Non-immutable data can be converted to immutable using function call in ctor

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21807

--- Comment #1 from Temtaime <temtaime at gmail.com> ---
Or at least
 Deprecation: slice of static array temporary returned by X assigned to longer
lived variable Y

--