test: Fix zlib-brotli output assumptions
On different architectures, it's possible for the compression algorithm to produce slightly different outputs. So, don't assume we will always get the same compressed output on all architectures. Instead, verify that the decompressing pre-compressed string functions correctly.
Fixes: https://github.com/nodejs/node/issues/25568
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
documentation is changed or added -
commit message follows commit guidelines