Suppress ExecutionContext flow in BeginErrorReadLine #2649

Job	Run time
build (macos-latest, Release)	1m 41s
build (windows-latest, Release)	3m 25s
build (windows-latest, Debug)	3m 8s
build (macos-latest, Debug)	1m 7s
build (ubuntu-latest, Release)	1m 30s
build (ubuntu-latest, Debug)	1m 19s
publish-coverage	0s
	12m 10s

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