workflow: split running tests required to be on the main thread

[eugenesvk]

into a separate workflow item with a custom argument so that the custom harness knows to use the main thread

Should hopefully fix the #128 test issues

[Byron]

Let's keep this as part of #128 - that's what it needs to run with to see if it has the desired effect. Please note that the osakit tests also have to bail (or fail) if they are not run on the main thread.

[eugenesvk]

Keeping it as part of 128 won't allow testing that pr since it will use the existing wrong workflow
I haven't errored on non-main thread just because it also sometimes works without the main thread

[Byron]

Keeping it as part of 128 won't allow testing that pr since it will use the existing wrong workflow

I don't understand why that would be. If you know of some restriction this repo might have, I am happy to lift it.
For all I know, PRs can change the workflow and observe the changes as well. Otherwise there would be no way to test these.

[eugenesvk]

Oh, seems your repo is already setup to work, you're right, guess the last time I've tried there was some issue that led to test failure