Limit unknown sources test to non-automotive

This change limist the `testUnknownSourcesOnByDefault` test to non-automotive environments only. The automotive vendors set the new user restriction 'no_install_unknown_sources'  which causes the obsolete install_non_market_apps' setting to flip to 0.

Bug: 325108796
Test: CtsProviderTestCases#android.provider.cts.settings.Settings_SecureTest#testUnknownSourcesOnByDefault

Change-Id: I0137a8457ed0cf6b62b4aaae657f5bd3ad818be9