Suppress ExecutionContext flow in BeginErrorReadLine #2633

Job	Run time
build (windows-latest, Release)	12m 27s
build (ubuntu-latest, Debug)	12m 47s
build (macos-latest, Debug)	6m 10s
build (macos-latest, Release)	7m 27s
build (windows-latest, Debug)	11m 54s
build (ubuntu-latest, Release)	14m 1s
publish-coverage	0s
	1h 4m 46s

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