[perl #40565] Fix localisation in pseudo-fork

Several SAVEt_* types were giving the SVs the wrong reference counts
in ss_dup, causing child process to lose SVs too soon.

See <https://rt.perl.org/Ticket/Display.html?id=40565#txn-1180404>
and <https://rt.perl.org/Ticket/Display.html?id=40565#txn-1277127>.
perldelta for the prev. commit

based on https://rt.perl.org/Ticket/Display.html?id=40565#txn-1321149