CONFDEV-47539 Use func-test-package 2.13.3, and use standard variable name for build overrides

https://server-syd-bamboo.internal.atlassian.com/browse/CBP-TIER2PLUGINS1-WEBDAV-70 is unhealthy even after merging my changes - although the failure cause has changed now. Still trying to work out why this build works so differently to the dedicated build. Could it be the testGroup batching causing issues?