andreas.braun noted in this comment:

the session/bug1274-002 test failed on the SHARDED_CLUSTER_RS deployment but passed on a subsequent run. We may want to keep an eye on this one.

========DIFF========
005+ Session is on server: no
005- Session is on server: yes
========DONE========
FAIL PHPC-1274: Session destruct should not end session from parent process [tests/session/bug1274-002.phpt] 

We should either modify the assertion for the session existing on the server or simply skip this test for sharded clusters (it's not particularly relevant to the driver functionality).