Improve help for --runxfail flag

The help for the '--runxfail' flag is somewhat misleading. The default
behaviour is to run tests marked as 'xfail' but to ignore the results. This
flag alters that behaviour by running these tests as if they weren't marked
'xfail', i.e. their results are not ignored.

changelog/5188.doc.rst

@@ -0,0 +1 @@
+Improve help for ``--runxfail`` flag.

src/_pytest/skipping.py

@@ -17,7 +17,7 @@ def pytest_addoption(parser):
         action="store_true",
         dest="runxfail",
         default=False,
-        help="run tests even if they are marked xfail",
+        help="report the results of xfail tests as if they were not marked",
     )
 
     parser.addini(