ci: using random order when doing the tests

[germa89]

Description

As the title. #GoodPractice

Issue linked

NA

Checklist

• I have visited and read Develop PyMAPDL.
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[SMoraisAnsys]

@germa89 While passing by... Would it make sense for you to use pytest-xdist ? This way you could speed up your tests by running them in parallel. If there is a limitation such that one worker has to work on a whole file, you can also use the option --dist loadfile so that each worker is provided with a test file and handling it totally.