Disable ffmpeg_test on COS.

This test mysteriously fails on Buildkite. Attempts to repro this failure in
similar environments failed. This test is still running on Ubuntu and works
fine on COS when manually tested.

PiperOrigin-RevId: 720726080

Author: ayushr2

Makefile

@@ -332,7 +332,8 @@ cos-gpu-all-tests: gpu-images cos-gpu-smoke-tests $(RUNTIME_BIN)
 	@$(call sudo,test/gpu:imagegen_test,--runtime=$(RUNTIME) -test.v --cos-gpu $(ARGS))
 	@$(call sudo,test/gpu:sr_test,--runtime=$(RUNTIME) -test.v --cos-gpu $(ARGS))
 	@$(call sudo,test/gpu:nccl_test,--runtime=$(RUNTIME) -test.v --cos-gpu $(ARGS))
-	@$(call sudo,test/gpu:ffmpeg_test,--runtime=$(RUNTIME) -test.v --cos-gpu $(ARGS))
+# TODO(b/392679618): Re-enable ffmpeg test.
+# @$(call sudo,test/gpu:ffmpeg_test,--runtime=$(RUNTIME) -test.v --cos-gpu $(ARGS))
 	@$(call sudo,test/gpu/vllm:vllm_test,--runtime=$(RUNTIME) -test.bench=. -test.benchtime=1x -cos-gpu -test.v $(ARGS))
 	@$(call sudo,test/gpu:sniffer_test,--runtime=$(RUNTIME) -test.v --cos-gpu $(ARGS))
 .PHONY: cos-gpu-all-tests