Increase number of orgs shown in the org selection drop-down menu

Seperate issue as requested in https://github.com/grafana/grafana/issues/78168#issuecomment-3558974474. See also https://github.com/grafana/grafana/issues/78168#issuecomment-3153321994. **Why is this needed**: The drop-down menu only shows about 4-5 entries at once since some update, which is difficult to use. We have 24+ orgs. **What would you like to be added**: I think it would help if the drop-down menu vertical size is increased to show more orgs at the same time, so that one has to do less "scroll down - stop scrolling - scan list - scroll down - stop scrolling - scan list" to find their org. **Who is this feature for?** Grafana Oraginzation Users