Expect RuntimeError or ValueError in ntequl test

Later versions of opm use a newer pybind11 version and potentially
different exceptions for input errors in its C++ backend. This makes
both `RuntimeError` and `ValueError` possible but tricky to pin down to
a particular opm version. This takes the easy route and allows for both.

tests/test_equil.py

@@ -475,8 +475,10 @@ def test_ntequl():
     df = equil.df(deckstr, ntequl=1)
     # We are not able to catch this situation..
     assert len(df) == 1
-    # But this will fail:
-    with pytest.raises(ValueError):
+    # But this will fail. Which exception is raised depends
+    # on the pybind11 version opm is built with which opm
+    # version is being used. Both are possible.
+    with pytest.raises((ValueError, RuntimeError)):
         equil.df(deckstr, ntequl=3)
 
     deckstr = """