Add mPackageParserCallback assignment in TestParams constructor

This is a fix for a revert of a revert at change ID
I4f5247f528f62c175bd34f0e4cb16c9456c8afe4.

It conflicts with Id53a2e65f6e5e4dee9a41cc77007275b3a220ac3, which
was merged before. That change moved the final callback field to
constructor assignment, so this fix does the same for the test
constructor.

Bug: 113638339

Test: build and atest PackageManagerComponentOverrideTests

Change-Id: Ia2c456335ad490ff3d555ed735edf3ae702ef836