[1.10.x] Fixed #26938 -- Fixed invalid HTML in template postmortem on the debug page.

Backport of 348cfccd90 from master

tests/view_tests/tests/test_debug.py

@@ -169,6 +169,14 @@ class DebugViewTests(LoggingCaptureMixin, SimpleTestCase):
             }]):
                 response = self.client.get(reverse('raises_template_does_not_exist', kwargs={"path": template_name}))
             self.assertContains(response, "%s (Source does not exist)" % template_path, status_code=500, count=2)
+            # Assert as HTML.
+            self.assertContains(
+                response,
+                '<li><code>django.template.loaders.filesystem.Loader</code>: '
+                '%s (Source does not exist)</li>' % os.path.join(tempdir, 'notfound.html'),
+                status_code=500,
+                html=True,
+            )
 
     def test_no_template_source_loaders(self):
         """