Suppress flaky multithreading swiftshader test
Suppress flaky multithreading swiftshader test

Bug: angleproject:5439
Change-Id: I218a4459897a9d543269effeea4caf05174e1589
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2577984
Reviewed-by: Shahbaz Youssefi <582eeec4f08a2ccd61e3ef52115e6e7c571582de@chromium.org>
Commit-Queue: Shahbaz Youssefi <582eeec4f08a2ccd61e3ef52115e6e7c571582de@chromium.org>

ppy/angle,ppy/angle,ppy/angle,ppy/angle