Switch the wikibase dumps to use the core database servers
We believe that the use of the analytics replica mariadb servers (dbstore100[7-9]) may be the cause of a performance regression affecting the wikibase dumps.
In order to test this theory, we want to change the value of the
SERVERGROUP environment variable from kube-dumps to main.
This will cause mediawiki-config to bypass the code that looks up the addresses and port numbers of the dbstore servers and adds them with a higher weight than the core servers.