eas_behaviour: Make TwoBigThreeSmallTask small task smaller
Reduce to 25% of a LITTLE CPU instead of 50% to match more closely the lisa legacy version of the test.
GitLab Maintenance scheduled for Thursday, 18th December 2025, from 7:00 AM to 10:00 AM BST. GitLab will be in read-only mode and experience short periods of complete downtime (up to 20 minutes) during this window.
Reduce to 25% of a LITTLE CPU instead of 50% to match more closely the lisa legacy version of the test.