Enable test to verify isRecursiveCopy of downloads and internal storage

This test has been disabled previously for being flaky locally.
Unfortunately it provides coverage for a rather large and critical code
block in the CopyJob. Let's enable it and watch the flakiness of it to
make it more robust instead of just disabling it.

Bug: 395926758
Flag: EXEMPT Test enablement
Test: atest testRecursiveCopyDocuments_InternalStorageToDownloadsProvider
Change-Id: I67cd6fa80afb02af795baedca82b515ab24f5371