Split up split test to collect artifacts correctly (#5785)

Summary:
Running two sets of test with the same name produces artefacts within the same directory,
which causes problems when collating the tests to folders.

Change-Id: I5da1b20ead1419c7593247aeb23ea560f33a575b

Pull Request resolved: https://github.com/pytorch/executorch/pull/5785

Reviewed By: mergennachin

Differential Revision: D63808459

Pulled By: digantdesai

fbshipit-source-id: bf24c7c2c24fcc9f4955f1df7207449309eef865