test: vars to const and let in child_process
Checklist
-
make -j4 test
(UNIX), orvcbuild test nosign
(Windows) passes -
commit message follows commit guidelines
Affected core subsystem(s)
test
Description of change
Replaced var keyword with const and let in some of the tests for child process stdin and stdio.
As part of https://github.com/nodejs/code-and-learn/issues/56