Fix failed test case for BatteryTip in Settings

- Replace the deprecated mocktio rule with MockitoJUnit.rule
- Fix the failed test cases
- Update the testing convention

Bug: 323627875
Test: atest SettingsRoboTests:com.android.settings.fuelgauge.batterytip
Change-Id: I25a39c8e7ad07482352c1e2152d8e16555429ab1