Fix Streamable HTTP Accept negotiation #1691

Job	Run time
checks / readme-snippets	15s
checks / pre-commit	39s
checks / test (3.10, lowest-direct, ubuntu-latest)	55s
checks / test (3.10, locked, ubuntu-latest)	49s
checks / test (3.11, lowest-direct, windows-latest)	2m 21s
checks / test (3.11, locked, ubuntu-latest)	52s
checks / test (3.10, lowest-direct, windows-latest)	2m 15s
checks / test (3.11, lowest-direct, ubuntu-latest)	58s
checks / test (3.11, locked, windows-latest)	2m 12s
checks / test (3.13, lowest-direct, ubuntu-latest)	52s
checks / test (3.14, locked, ubuntu-latest)	2m 13s
checks / test (3.13, lowest-direct, windows-latest)	2m 55s
checks / test (3.10, locked, windows-latest)	2m 12s
checks / test (3.12, lowest-direct, windows-latest)	3m 25s
checks / test (3.12, locked, ubuntu-latest)	54s
checks / test (3.12, locked, windows-latest)	3m 10s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 0s
checks / test (3.13, locked, windows-latest)	2m 7s
checks / test (3.13, locked, ubuntu-latest)	49s
checks / test (3.14, locked, windows-latest)	2m 52s
checks / test (3.14, lowest-direct, windows-latest)	2m 7s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 12s
all-green	2s
	37m 6s

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