Shorten sleep for racy run-test 063.

Didn't look closely enough to know exactly why this needs to be
shortened, but I've verified that it fixes the case where we run with:
--interpreter, --optimizing, and --gcstress.

Bug: 2310700
Test: ./art/test/testrunner/run_build_test_target.py -j110
art-read-barrier-gcstress

Change-Id: Ic82f1bbb178c0debdfafc260084e760df226e298