Fix broken test on GSI branch

Both com.android.apex.cts.shim.v2_prebuilt and StagedInstallTestApexV2
provide the same artifact. Tests that are using StagedInstallTestApexV2
are passing, whereas tests using com.android.apex.cts.shim.v2_prebuilt
are failing.

Root cause has not been identified yet. Proactively swapping the targets
to get the test green.

Bug: 200737517
Test: atest StagedInstallInternalTest#testAdbStagedReadyWaitCanBeSkipped
Change-Id: Ibdd72ec062538838ad60b847ee1ff31a792520a3