test: fix inspector tests

The inspector tests should not be in the parallel directory as they
likely all (or certainly almost all) use static ports, so port
collisions will happen.

This moves them all to sequential. We can move them back on a
case-by-case basis. They were run sequentially when they were in the
inspector directory which they were only moved from very recently.

PR-URL: https://github.com/nodejs/node/pull/16281


Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Bryan English <bryan@bryanenglish.com>