validate_that_environment_sim_folder_is_writeable doesn't fail on unwritable folders

[achaikou]

I would expect everest to raise error not only when there is no writeable directory on the simulation directory path, but also when simulation directory alone is not writeable.
Current verifications seem intended (maybe for non-existent paths only?), so I am not 100% certain.

For the moment test placeholder test_that_simulation_folder_without_write_access_raises_validation_error is created as x-fail (see #14055)

[eqbech]

What is the purpose of this validation? I cant make sense of what it is checking.