[8.0] updating the mysql version used in the tests

[fstagni]

From 8.0 to 8.4

Changes to port to wiki:

ALTER TABLE Tasks DROP PRIMARY KEY, ADD PRIMARY KEY (`TaskID`);
ALTER TABLE CacheReplicas DROP PRIMARY KEY, ADD PRIMARY KEY (`ReplicaID`);

BEGINRELEASENOTES

*Subsystem
CHANGE: default MySQL version from 8.0 to 8.4

ENDRELEASENOTES