As of commit bb767a7, Pacemaker's iso8601 command line tool is deprecated. pcs is currently the only known user.
It should be removed at a compatibility break when a suitable amount of time has passed, and after we no longer support any OS distro with a pcs version that requires it.
See also the following RHEL issue for pcs:
- RHEL-113368: Drop uses of Pacemaker's iso8601 command line tool