test: move test-http-max-http-headers to parallel

test-http-max-http-headers seems to run fine in parallel, even with
`tools/test.py -j 96 --repeat 192
test/parallel/test-http-max-http-headers.js`.

The same applies to `test-set-http-max-http-headers.js` which (as
written) depends on `test-http-max-http-headers.js` being in the same
directory. So that is being moved too.

PR-URL: https://github.com/nodejs/node/pull/30712


Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>