Skip broken HTML preview test case with libxml >= 2.14

The `test_no_tree` test case is known to fail with libxml >= 2.14, so
skip it for the time being when libxml >= 2.14 is used.

Reported-by: Ivan Shapovalov <[email protected]>
Ref: https://gitlab.gnome.org/GNOME/libxml2/-/issues/908
Tested-by: Pascal Ernster <[email protected]>
Closes: #18406
Signed-off-by: Pascal Ernster <[email protected]>

Author: hardfalcon

changelog.d/18413.bugfix

@@ -0,0 +1 @@
+Skip broken HTML preview test case with libxml >= 2.14.

tests/media/test_html_preview.py

@@ -27,9 +27,11 @@
 )
 
 from tests import unittest
+from unittest.case import SkipTest
 
 try:
     import lxml
+    from lxml import etree
 except ImportError:
     lxml = None  # type: ignore[assignment]
 
@@ -324,6 +326,9 @@ def test_empty(self) -> None:
 
     def test_no_tree(self) -> None:
         """A valid body with no tree in it."""
+        if etree.LIBXML_VERSION >= (2, 14):
+            raise SkipTest("This test is known to be broken with lixml >= 2.14.")
+
         html = b"\x00"
         tree = decode_body(html, "http://example.com/test.html")
         self.assertIsNone(tree)