Properly mock PackageManager#getPackageInfo

Because this method is non-null method, the mock should not return null.
To prevent the test crashing, this adds a mock.

Bug: 424369501
Test: HearingDevicesDialogDelegateTest
Flag: com.android.hardware.input.mouse_to_touch_per_app_compat
Change-Id: Icb5d5bd3646bcc61264eefa78a33640118badc46