Ensure that hadd python tests are run only if pytest is available

[LukasBreitwieser]

Change CMake function from ROOTTEST_ADD_TEST to ROOT_ADD_PYUNITTEST

[github-actions]

Test Results

    20 files      20 suites   3d 17h 20m 5s ⏱️
 3 038 tests  3 038 ✅ 0 💤 0 ❌
59 166 runs  59 166 ✅ 0 💤 0 ❌

Results for commit 3f009ad.

[guitargeek]

Thank you very much!

[linev]

Hi,

There are one problem using ROOT_ADD_PYUNITTEST test.
If python script runs in source directory - it also creates __pycache__ subdirectory deep in root sources.
To avoid this - one should copy first python script to build directory.
Therefore one need to modify ROOT_ADD_PYUNITTEST macro.