Configure existing WPP2 Robolectric tests to run with atest. am: f55c70bdfc

Original change: https://android-review.googlesource.com/c/platform/packages/apps/WallpaperPicker2/+/2328377

Change-Id: Ic0958019f461397331e9a82f1e51d13ef20e8841
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>