[perl #132353] [LTA] error with using meta assign ops with bound SetHash

[via RT]

# New Ticket Created by  Zoffix Znet 
# Please include the string:  [perl #132353]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=132353 >


This code produces an LTA error:

    my %days := SetHash.new: Date.today … Date.new: '2030-04-02';
    %days ∖= %days.grep: *.key.day-of-week > 5;

First, the error reads "Cannot modify an immutable SetHash" which is confusing,
since SetHash is a mutable type.

Second, the error dumps all of the contents of the SetHash, so for this code,
the user has to scroll several pages up just to get to the error itself.