Summary:
The `RollbackYsqlMajorVersionUpgrade` RPC is synchronous and can take a long time to complete. The test was failing because the timeout was too short. This change increases the timeout to 3 minutes.

Fixes #24361
Jira: DB-13274

Test Plan: UpgradeFrom_2_20_2_4/BasicUpgradeTest.TestRollback/0

Reviewers: tfoucher, smishra

Reviewed By: tfoucher

Subscribers: ybase

Tags: #jenkins-ready

Differential Revision: https://phorge.dev.yugabyte.com/D38899