test_graph.py::test_guess_format_for_parse_http_text_plain regression

[gjhiggins]

A recently-introduced URL in test/test_graph/test_graph.py is returning 406: Not Acceptable causing test_guess_format_for_parse_http_text_plain to fail:

poetry run pytest test/test_graph/test_graph.py::test_guess_format_for_parse_http_text_plain

I fixed this locally by swapping out the github URL for a W3C URL:

diff --git a/test/test_graph/test_graph.py b/test/test_graph/test_graph.py
index 1c95b05f..092199e5 100644
--- a/test/test_graph/test_graph.py
+++ b/test/test_graph/test_graph.py
@@ -399,7 +399,8 @@ def test_guess_format_for_parse_http_text_plain():
     assert len(graph) > 0
 
     # A url that returns content-type text/html.
-    url = "https://github.com/RDFLib/rdflib/issues/2734"
+    # url = "https://github.com/RDFLib/rdflib/issues/2734"
+    url = "https://www.w3.org/TR/REC-rdf-syntax/"
     with pytest.raises(PluginException):
         graph = Graph().parse(url)