Three ri_wellmod tests fail when executed on github online runners

[andreas-el]

When removing pytestmark = pytest.mark.xfail() three tests fail when run on the GitHub online runners.
The same tests pass using rhel8 tgx or rhel8 linapp-nodes.

FAILED tests/test_ri_wellmod.py::test_main_inputcase - AssertionError: assert (False)
 +  where False = <bound method Path.exists of PosixPath('welldefs_inputcase.sch')>()
 +    where <bound method Path.exists of PosixPath('welldefs_inputcase.sch')> = PosixPath('welldefs_inputcase.sch').exists
 +      where PosixPath('welldefs_inputcase.sch') = Path('welldefs_inputcase.sch')
FAILED tests/test_ri_wellmod.py::test_main_initcase_reek - AssertionError: assert (False)
 +  where False = <bound method Path.exists of PosixPath('welldefs_initcase_reek.sch')>()
 +    where <bound method Path.exists of PosixPath('welldefs_initcase_reek.sch')> = PosixPath('welldefs_initcase_reek.sch').exists
 +      where PosixPath('welldefs_initcase_reek.sch') = Path('welldefs_initcase_reek.sch')
FAILED tests/test_ri_wellmod.py::test_main_lgr_reek - AssertionError: assert (False)
 +  where False = <bound method Path.exists of PosixPath('welldefs_lgr_reek.sch')>()
 +    where <bound method Path.exists of PosixPath('welldefs_lgr_reek.sch')> = PosixPath('welldefs_lgr_reek.sch').exists
 +      where PosixPath('welldefs_lgr_reek.sch') = Path('welldefs_lgr_reek.sch')
= 3 failed, 767 passed, 36 skipped, 1 xfailed, 16 warnings in 327.96s (0:05:27) =