macOS mktemp doesn't accept --suffix

[awwright]

Trying to run the program on macOS 15.5, I get the error:

mktemp: unrecognized option `--suffix=.json'
usage: mktemp [-d] [-p tmpdir] [-q] [-t prefix] [-u] template ...
       mktemp [-d] [-p tmpdir] [-q] [-u] -t prefix 
/Users/awright/gentoo-ami-builder/lib/app-lib.sh: line 226: : No such file or directory

It appears macOS "mktemp" doesn't support the --suffix option. Simply removing it seems to fix the problem, as the .json suffix is nice, but not strictly necessary for the aws cli's needs.