Remove 'not' from check as we want to skip if python version is below…

… 3.8 (#162)

Co-authored-by: Michael Richard Mckinsey <mckinsey@quartz1148.llnl.gov>

thicket/tests/test_model_extrap.py

@@ -23,7 +23,7 @@
 except ImportError:
     extrap_avail = False
 
-if not sys.version_info < (3, 8):
+if sys.version_info < (3, 8):
     pytest.skip(
         "requires python3.8 or greater to use extrap module", allow_module_level=True
     )