ci: Remove -j# from test options

[floatingatoll]

We have what looks to be a CI failure due to a race condition between two different sets of tests that expect to be using a given port number, so this patch removes all parallelization from the tests (which is how I kept them for most of my repairs anyways). HT @gcoxmoz

[bkochendorfer]

I rediscovered this and merged a similar change! I wish I had remembered this yesterday haha