Use AAPT2 For SettingsUnitTests

Forces tradefed to use aapt2 for SettingsUnitTests to get around
the issue of Settings.apk not being parseable by aapt.

Bug: 247779071
Test: atest SettingsUnitTests
Change-Id: I8af260f8d2c438512d3e61f0028accf7b40c8a00
1 file changed