Enable `VideoReceiveStreamTestWithFakeDecoder.RenderedFrameUpdatesGetSources` for iOS.

This change re-enables a previously flaky unit tests for iOS. It seems to have the same root cause as webrtc:10827 and which was fixed by: https://webrtc-review.googlesource.com/c/src/+/149171

Bug: webrtc:10872, webrtc:10827
Change-Id: I71b2581cf8c75e0dd6a39b77e6cf34c121ff22f4
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/149802
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Jonas Oreland <jonaso@webrtc.org>
Commit-Queue: Chen Xing <chxg@google.com>
Cr-Commit-Position: refs/heads/master@{#28893}