fix(streamable-http): downgrade stateless 'Terminating session: None' log #2517

Job	Run time
checks / pre-commit	37s
checks / readme-snippets	10s
checks / test (3.11, lowest-direct, ubuntu-latest)	47s
checks / test (3.11, locked, windows-latest)	1m 14s
checks / test (3.10, locked, windows-latest)	1m 23s
checks / test (3.11, locked, ubuntu-latest)	50s
checks / test (3.10, locked, ubuntu-latest)	51s
checks / test (3.13, lowest-direct, windows-latest)	1m 46s
checks / test (3.10, lowest-direct, ubuntu-latest)	57s
checks / test (3.12, lowest-direct, windows-latest)	1m 45s
checks / test (3.14, lowest-direct, windows-latest)	1m 6s
checks / test (3.10, lowest-direct, windows-latest)	1m 16s
checks / test (3.12, locked, ubuntu-latest)	37s
checks / test (3.12, locked, windows-latest)	1m 28s
checks / test (3.11, lowest-direct, windows-latest)	1m 16s
checks / test (3.13, locked, windows-latest)	1m 13s
checks / test (3.14, lowest-direct, ubuntu-latest)	45s
checks / test (3.13, lowest-direct, ubuntu-latest)	49s
checks / test (3.13, locked, ubuntu-latest)	47s
checks / test (3.14, locked, ubuntu-latest)	1m 50s
checks / test (3.14, locked, windows-latest)	2m 30s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 1s
all-green	3s
	25m 1s

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