ci: run 5 partitions for tests (#4389)

* ci: run 4 partitions for tests

* run 5

* revert retry update

* reduce the timeout

.buildkite/scripts/build-stable.sh

@@ -13,9 +13,9 @@ partitions=$(
 {
   "name": "partitions",
   "command": "ci/docker-run-default-image.sh ci/stable/run-partition.sh",
-  "timeout_in_minutes": 30,
+  "timeout_in_minutes": 25,
   "agent": "$agent",
-  "parallelism": 2,
+  "parallelism": 5,
   "retry": 3
 }
 EOF