tests/sys/cddl: correctly quote atf_set "require.progs"
The argument has to be a single whitespace-separate value. While touching
all these lines also add ksh93, since atf_set "require.progs" overrides
the default value specified in the Kyuafile. This then results in tests
being executed despite ksh93 not being installed.
Reviewed By: asomers
Differential Revision: https://reviews.freebsd.org/D29066