Disable RTCVideoRenderFrameCallbackNV12 test

It has been crashing on trybots

BUG=webrtc:7863
TBR=magjed@webrtc.org
NOTRY=True

Review-Url: https://codereview.webrtc.org/2951273002
Cr-Commit-Position: refs/heads/master@{#18720}
diff --git a/webrtc/sdk/objc/Framework/UnitTests/RTCMTLVideoViewTests.mm b/webrtc/sdk/objc/Framework/UnitTests/RTCMTLVideoViewTests.mm
index 99004ea..a5fb15a 100644
--- a/webrtc/sdk/objc/Framework/UnitTests/RTCMTLVideoViewTests.mm
+++ b/webrtc/sdk/objc/Framework/UnitTests/RTCMTLVideoViewTests.mm
@@ -178,7 +178,8 @@
   [test tearDown];
 }
 
-TEST(RTCMTLVideoViewTests, RTCVideoRenderFrameCallbackNV12) {
+// The test is disabled because of frequent crashes. See bugs.webrtc.org/7863
+TEST(RTCMTLVideoViewTests, DISABLED_RTCVideoRenderFrameCallbackNV12) {
   RTCMTLVideoViewTests *test = [[RTCMTLVideoViewTests alloc] init];
   [test setup];