Fix ParallelizableAttribute with TestFixtureSource

[jairbubbles]

Tests declared like that:

[TestFixtureSource("Data")]
[Parallelizable(ParallelScope.All)]
public class TestFixtureSourceWithParallelizableAttribute

were no longer run in parallel since that change: 247ede8

Similar to #3715 I explicitely apply ParallelizableAttribute to children tests.

Closes #3735

NB: I couldn't run tests in master branch so I tested in the 3.0 dev branch.

[jontdelorme]

Hello, we are waiting for that fix to update to the latest version. Anyone ready for the review?

[jairbubbles]

Hey @SimonCropp anything I can do to get this merged?

[SimonCropp]

@jairbubbles LGTM. but i am not a maintainer on this project, so cant merge

[jairbubbles]

Oh sorry I found your name in the last PRs merged but I guess you were just the author then.

[jairbubbles]

(Thx @stevenaw for updating my branch)

[jairbubbles]

Hi @stevenaw, anything I can do to help this PR getting merged?

[stevenaw]

Hi @jairbubbles thanks for asking. Nothing on your end, this just needs a review by the team. Sorry it's taken so long to be looked at. I'd hoped to review it but I got a little unexpectedly busy myself. I still hope to get to this soon.

[OsirisTerje]

@stevenaw This looks very simple. Do you think we can just merge it?

[stevenaw]

I'd be alright with that @OsirisTerje
This LGTM too, thanks @jairbubbles for your contribution!

[stevenaw]

I'm having a bit of a hard time merging.

[jairbubbles]

I rebased and resolved the conflict manually.