Fix test failure with updated lxml

Author: kovidgoyal

src/calibre/library/comments.py

@@ -165,7 +165,9 @@ def test_comments_to_html(self):
                     ('a <?xml asd> b\n\ncd',
                         '<p class="description">a  b</p><p class="description">cd</p>'),
             ]:
-                cval = comments_to_html(pat)
+                import warnings  # lxml + beautifulsoup raise a deprecation warning causing test to fail in CI
+                with warnings.catch_warnings():
+                    cval = comments_to_html(pat)
                 self.assertEqual(cval, val)
 
     return unittest.defaultTestLoader.loadTestsFromTestCase(Test)