UCX w/ MPI deadlocking in CI

[davidozog]

This row:
UCX (--enable-pmi-mpi CC=mpicc --disable-fortran)

Example here:
https://github.com/Sandia-OpenSHMEM/SOS/runs/5650454734?check_suite_focus=true

[davidozog]

I haven't seen this failure in a long time - it may be a false positive.

[davidozog]

This issue recurred at least twice in PR #1108, so reopening the issue for now. In one case on the spec-example test shmem_team_broadcast deadlocked.

We may prefer to disable or swap out this test row until it's resolved because it can slow down PR procedures considerably.

[davidozog]

Seeing another instance of probable deadlock on PR #1106, on unit test cxx_test_shmem_put I think.