http2: keep reading during small client writes #6096

Job	Run time
Build slim tarball	2m 41s
collect-openssl-versions	7s
aarch64-darwin: with shared libraries	24m 4s
aarch64-linux: Cache V8 build	5s
x86_64-darwin: with shared libraries	1h 0m 0s
x86_64-linux: with shared libraries	30m 46s
aarch64-linux: with shared openssl_1_1 (1.1.1w)	24m 16s
aarch64-linux: with shared openssl_3_6 (3.6.1)	24m 49s
aarch64-linux: with shared openssl_3 (3.0.19)	25m 4s
aarch64-linux: with shared openssl_3_5 (3.5.5)	25m 39s
aarch64-linux: with shared openssl_4_0 (4.0.0)	24m 33s
	4h 2m 4s

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