JobScheduler: Add missing unit tests for job name.

Addresses the lack of unit tests for job name construction, providing
more confidence in future changes.

Bug: 354795473
Test: atest FrameworksMockingServicesTests:com.android.server.job
Test: atest CtsJobSchedulerTestCases
Flag: EXEMPT bugfix
Change-Id: I6a980e1312ecdc25cccbc2d6b87a029a2e1a14de