message: Fix race condition in tests
  Summary:
  This is a race condition which somtimes causes CI failures.
  Ref T16509
  Test Plan: Tests pass locally
  Reviewers: davidn, #tensorflow, simonl, #framework_ip_review_-_any_oss_or_third-party_code_use_has_been_approved
  Maniphest Tasks: T16509
diff: @@ -64,7 +64,8 @@ class IpuIpuModelTest(xla_test.XLATestCase):
  fd = {pa: [[1., 1.], [2., 3.]], pb: [[0., 1.], [4., 5.]]}
  sess.run(report, fd)
  - result, rep = sess.run([output, report], fd)
  + result = sess.run(output, fd)
  + rep = sess.run(report, fd)
  self.assertAllClose(result, [[1., 2.], [6., 8.]])
  self.assertTrue(len(rep) == 0)
  @@ -84,7 +85,8 @@ class IpuIpuModelTest(xla_test.XLATestCase):
  fd = {pa: [[1., 1.], [2., 3.]], pb: [[0., 1.], [4., 5.]]}
  sess.run(report, fd)
  - result, rep = sess.run([output, report], fd)
  + result = sess.run(output, fd)
  + rep = sess.run(report, fd)
  self.assertAllClose(result, [[1., 2.], [6., 8.]])
  types = r.parse_events(rep, assert_len=4)
  @@ -114,7 +116,9 @@ class IpuIpuModelTest(xla_test.XLATestCase):
  result = sess.run(out1, fd)
  self.assertAllClose(result, [[1., 2.], [6., 8.]])
  - result, rep = sess.run([out2, report], fd)
  + result = sess.run(out2, fd)
  + rep = sess.run(report, fd)
  +
  self.assertAllClose(result, [[1., 0.], [-2., -2.]])
  # 2x engine, 2x compile_begin, 2x compile_end, 2x load engine
  