doc: improve doc writable streams: 'finish' event.
Change order for 'finish' event that should be before writer.end. Fixes: https://github.com/nodejs/node/issues/30759
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