test: enable spawn tests for ch4:ucx

The spawn tests are disabled previously. Let's enable them.

Author: hzhou

test/mpi/configure.ac

@@ -481,7 +481,6 @@ if test "$MPI_IS_MPICH" = "yes" ; then
         elif [grep 'MPICH Device:[[:blank:]]*ch4:ucx' conftest.output > /dev/null] ; then
             AC_MSG_NOTICE([Detected MPICH with ch4:ucx netmod])
             AC_DEFINE(MPICH_CH4_UCX, 1, [define if it is mpich with ch4:ucx])
-            enable_spawn=no
         elif [grep 'MPICH Device:[[:blank:]]*ch3' conftest.output > /dev/null] ; then
             enable_part=no
         fi