zlib: validate flush kind for brotli streams #7672

Job	Run time
Build slim tarball	1m 8s
aarch64-darwin: with shared libraries	27m 3s
x86_64-darwin: with shared libraries	49m 34s
aarch64-linux: Cache V8 build	22s
x86_64-linux: with shared libraries	27m 27s
aarch64-linux: with shared openssl-4.0.0	24m 43s
aarch64-linux: with shared openssl-3.5.6	24m 26s
aarch64-linux: with shared openssl-3.0.20	23m 58s
aarch64-linux: with shared openssl-1.1.1w	23m 41s
aarch64-linux: with shared openssl-3.6.2	24m 9s
aarch64-linux: with shared boringssl-0.20260508.0	23m 49s
	4h 10m 20s

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