fix: Streamable HTTP Accept negotiation handling #3617

Job	Run time
checks / pre-commit	1m 3s
checks / readme-snippets	12s
checks / docs	51s
checks / test (3.11, lowest-direct, windows-latest)	1m 14s
checks / test (3.10, lowest-direct, windows-latest)	3m 3s
checks / test (3.10, locked, windows-latest)	2m 33s
checks / test (3.10, locked, ubuntu-latest)	1m 26s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 23s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 3s
checks / test (3.11, locked, windows-latest)	1m 56s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 18s
checks / test (3.12, lowest-direct, windows-latest)	1m 59s
checks / test (3.14, locked, windows-latest)	2m 0s
checks / test (3.14, locked, ubuntu-latest)	1m 17s
checks / test (3.13, locked, ubuntu-latest)	1m 18s
checks / test (3.11, locked, ubuntu-latest)	1m 21s
checks / test (3.14, lowest-direct, windows-latest)	2m 59s
checks / test (3.13, lowest-direct, windows-latest)	1m 58s
checks / test (3.12, locked, ubuntu-latest)	1m 40s
checks / test (3.13, locked, windows-latest)	1m 51s
checks / test (3.12, locked, windows-latest)	3m 11s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 29s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 7s
all-green	2s
	38m 14s

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