Fix SendRequestAsync hang on Streamable HTTP SSE retry #2357

Job	Run time
build (windows-latest, Debug)	11m 39s
build (macos-latest, Debug)	5m 4s
build (ubuntu-latest, Debug)	12m 52s
build (windows-latest, Release)	9m 26s
build (ubuntu-latest, Release)	11m 58s
build (macos-latest, Release)	5m 30s
publish-coverage	0s
	56m 29s

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