fix flaky GPU test

Summary:
Relaxed a test slightly to avoid transient failures.
Errors here:
https://www.internalfb.com/intern/testinfra/diagnostics/5066549780888824.844425016185500.1695878046/
https://www.internalfb.com/intern/testinfra/diagnostics/16044073676393084.844425016185500.1695809788/

Reviewed By: mlomeli1

Differential Revision: D49726244

fbshipit-source-id: 6c55efb8ff5b470dbd426129cb12fb9a0b40939f

Author: mdouze

faiss/gpu/test/test_multi_gpu.py

@@ -89,7 +89,8 @@ def do_test_sharded_ivf(self, index_key):
         index.add(ds.get_database())
 
         Dnew8, Inew8 = index.search(ds.get_queries(), 10)
-        np.testing.assert_array_equal(Iref8, Inew8)
+        # np.testing.assert_array_equal(Iref8, Inew8)
+        self.assertLess((Iref8 != Inew8).sum(), Iref8.size * 0.003)
         np.testing.assert_array_almost_equal(Dref8, Dnew8, decimal=4)
 
     def test_sharded_IVFSQ(self):