test: set umask for tests

https://github.com/nodejs/node/pull/25213 proposes setting umask in the
Python test runner to avoid spurious test failures when running from a
shell with a restrictive umask. This is a good idea, but will only fix
the issue for tests run with the Python runner. Set it in
`common/index.js` as well so that it fixes it even when tests are run
directly with a `node` binary, bypassing the Python test runner.

PR-URL: https://github.com/nodejs/node/pull/25229


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>