Use calculator instead of Gmail in UnminimizeAppFromTaskbar

When launching GMail we expect to open the Activity
ConversationListActivityGmail, but gmail might enter another Activity
before that if for example the test device has no logged-in account.
Instead use the calculator that doesn't have log-in screen.

Bug: 399420941
Test: atest PlatformScenarioTests:UnminimizeAppFromTaskbarTest
Flag: EXEMPT - test fix
Change-Id: I7c24d552ad19ba662db950f1bd9596eb4f270760