test: move test-vm-break-on-sigint to sequential

This PR moves `test-vm-break-on-sigint.js` to sequential, following the
other PRs I have made to move CPU intensive tests into sequential. The
test has already been tuned to do less iterations in a previous PR.
However it is still causing ~7% of build failures. The timeouts seem
highly correlated with other tests which spawn a bunch of threads also
failing, see for example the [first Jenkins failure][] and the [last
Jenkins failure][].

[first Jenkins failure]: https://ci.nodejs.org/job/node-test-pull-request/45756/
[last Jenkins failure]: https://ci.nodejs.org/job/node-test-pull-request/45837/

Refs: nodejs#44090
Refs: nodejs#43981
Refs: nodejs/reliability#337
PR-URL: nodejs#44140
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: theanarkh <[email protected]>
Reviewed-By: Feng Yu <[email protected]>

Author: kvakil