MM-43653: Fix incorrect system store update (#20051)

https://mattermost.atlassian.net/browse/MM-43653

```release-note
NONE
```

store/sqlstore/system_store.go

@@ -78,7 +78,7 @@ func (s SqlSystemStore) SaveOrUpdateWithWarnMetricHandling(system *model.System)
 }
 
 func (s SqlSystemStore) Update(system *model.System) error {
-	query := "UPDATE Systems SET Name=:Name, Value=:Value"
+	query := "UPDATE Systems SET Value=:Value WHERE Name=:Name"
 	if _, err := s.GetMasterX().NamedExec(query, system); err != nil {
 		return errors.Wrapf(err, "failed to update system property with name=%s", system.Name)
 	}