stream: fix Writable.toWeb() hang on synchronous drain #6995

Job	Run time
Build slim tarball	1m 11s
aarch64-linux: Cache V8 build	29s
x86_64-linux: with shared libraries	24m 21s
x86_64-darwin: with shared libraries	36m 1s
aarch64-darwin: with shared libraries	24m 35s
aarch64-linux: with shared openssl-3.5.5	22m 20s
aarch64-linux: with shared openssl-3.0.19	23m 3s
aarch64-linux: with shared openssl-1.1.1w	24m 13s
aarch64-linux: with shared boringssl-0.20260413.0	23m 26s
aarch64-linux: with shared openssl-4.0.0	22m 20s
aarch64-linux: with shared openssl-3.6.1	23m 22s
	3h 45m 21s

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