[TESTING] Switch to ParallelTestRunner.jl

[aelligp]

Whats the purpose of this PR?

• Bug fix
• New feature
• Documentation update
• Other, please explain

Describe it in more detail below:
Switching to ParallelTestRunner.jl to speed up the tests and fix a few things that didnt quite work.

Checklist

• The PR title is descriptive and starts with the appropriate tag: [BUGFIX], [ADDITION], [DOC], etc.
• New tests (either assessing the correct behaviour of new internal functions or the correctness of a tutorial) were added, or old tests were updated
• Affected tutorials have also been updated
• The new feature was added in a way that does not break public API
• New documentation related to the new feature was added
• The new code follows the contributor guidelines, in particular the Runic Style

[github-actions]

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