HBASE-22911 reduce concurrent PR builds.
HBASE-22911 reduce concurrent PR builds.

Signed-off-by: Duo Zhang <ca823f7b4f21a31b6ef7892c1f90d53103f0d135@apache.org>

HubSpot/hbase,HubSpot/hbase,HubSpot/hbase,HubSpot/hbase,HubSpot/hbase,HubSpot/hbase,HubSpot/hbase,HubSpot/hbase,HubSpot/hbase,HubSpot/hbase