CVE-2024-56406: Heap-buffer-overflow with tr//

This was due to underallocating needed space.  If the translation forces
something to become UTF-8 that is initially bytes, that UTF-8 could
now require two bytes where previously a single one would do.

(cherry picked from commit f93109c8a6950aafbd7488d98e112552033a3686)

Author: khwilliamson

op.c

@@ -6881,6 +6881,7 @@ S_pmtrans(pTHX_ OP *o, OP *expr, OP *repl)
                  * same time.  But otherwise one crosses before the other */
                 if (t_cp < 256 && r_cp_end > 255 && r_cp != t_cp) {
                     can_force_utf8 = TRUE;
+                    max_expansion = MAX(2, max_expansion);
                 }
             }