test: skip the uproot end-to-end fill when uproot lacks uproot.graphed

An installed uproot without the graphed reader (any release before scikit-hep/uproot5#1720) raised AttributeError instead of skipping.

Assisted-by: ClaudeCode:claude-fable-5-1

Author: lgray

tests/test_graphed.py

@@ -136,6 +136,8 @@ def read_partition(self, partition, _columns, _resources):
 
 def test_uproot_ttree_fill_end_to_end():
     uproot = pytest.importorskip("uproot")
+    if not hasattr(uproot, "graphed"):
+        pytest.skip("uproot without uproot.graphed (scikit-hep/uproot5#1720)")
     pytest.importorskip("graphed.awkward")
     skhep_testdata = pytest.importorskip("skhep_testdata")