Skip test_glibc_version_string_ctypes_raise_oserror if ctypes is …

…unavailable (#741)

Co-authored-by: Kevin Chang <kevin.chang2@capitalone.com>

tests/test_manylinux.py

@@ -140,6 +140,7 @@ def test_glibc_version_string_ctypes_missing(monkeypatch):
     assert _glibc_version_string_ctypes() is None
 
 
+@pytest.mark.xfail(ctypes is None, reason="ctypes not available")
 def test_glibc_version_string_ctypes_raise_oserror(monkeypatch):
     def patched_cdll(name):
         raise OSError("Dynamic loading not supported")