fix(streamable-http): downgrade stateless 'Terminating session: None' log #2518

Job	Run time
checks / readme-snippets	13s
checks / pre-commit	40s
checks / test (3.11, lowest-direct, ubuntu-latest)	49s
checks / test (3.11, lowest-direct, windows-latest)	1m 30s
checks / test (3.12, locked, ubuntu-latest)	52s
checks / test (3.12, locked, windows-latest)	1m 30s
checks / test (3.11, locked, ubuntu-latest)	49s
checks / test (3.11, locked, windows-latest)	1m 43s
checks / test (3.10, locked, windows-latest)	1m 17s
checks / test (3.10, lowest-direct, ubuntu-latest)	50s
checks / test (3.10, locked, ubuntu-latest)	47s
checks / test (3.13, lowest-direct, ubuntu-latest)	55s
checks / test (3.12, lowest-direct, windows-latest)	1m 21s
checks / test (3.10, lowest-direct, windows-latest)	1m 29s
checks / test (3.12, lowest-direct, ubuntu-latest)	54s
checks / test (3.14, locked, windows-latest)	2m 7s
checks / test (3.13, locked, windows-latest)	1m 15s
checks / test (3.14, lowest-direct, windows-latest)	1m 24s
checks / test (3.14, locked, ubuntu-latest)	1m 51s
checks / test (3.13, locked, ubuntu-latest)	44s
checks / test (3.14, lowest-direct, ubuntu-latest)	46s
checks / test (3.13, lowest-direct, windows-latest)	1m 48s
all-green	5s
	25m 39s

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