stream: fix Writable.toWeb() hang on synchronous drain #7066

Job	Run time
Build slim tarball	1m 14s
aarch64-linux: Cache V8 build	24s
x86_64-linux: with shared libraries	27m 16s
aarch64-darwin: with shared libraries	24m 0s
x86_64-darwin: with shared libraries	40m 21s
aarch64-linux: with shared boringssl-0.20260413.0	24m 44s
aarch64-linux: with shared openssl-3.6.1	25m 14s
aarch64-linux: with shared openssl-4.0.0	25m 11s
aarch64-linux: with shared openssl-3.0.19	24m 57s
aarch64-linux: with shared openssl-1.1.1w	24m 31s
aarch64-linux: with shared openssl-3.5.5	25m 28s
	4h 3m 20s

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