Disable flaky ModelDownloader integration tests. am: 5247b140e9

Original change: https://googleplex-android-review.googlesource.com/c/platform/external/libtextclassifier/+/23472318

Change-Id: I26ce1f653d94d9b984444c51b651d03d324d1235
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>