test: make test-v8-serdes work without stdin
If stdin
was closed or referred to a file, this didn't work,
because it was accessed via file descriptor.
Instead, use another generic native object.
cherry-picked from ayojs/ayo#63
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
commit message follows commit guidelines
Affected core subsystem(s)
test