find-arch-on-crt.sh: adjust for patsub_replacement

This shell behavior[1] in Bash 5.2 "expands occurrences of '&' in the
replacement string of pattern substitution to the text matched by the
pattern" but we want literal ampersands so escape them.

[1] https://www.gnu.org/software/bash/manual/html_node/The-Shopt-Builtin.html