Skip test which fails randomly on Python 2.7 (#32569)

lib/spack/spack/test/concretize.py

@@ -1528,6 +1528,9 @@ def test_delete_version_and_reuse(self, mutable_database, repo_with_changing_rec
         assert root.dag_hash() == new_root.dag_hash()
 
     @pytest.mark.regression("29201")
+    @pytest.mark.skipif(
+        sys.version_info[:2] == (2, 7), reason="Fixture fails intermittently with Python 2.7"
+    )
     def test_installed_version_is_selected_only_for_reuse(
         self, mutable_database, repo_with_changing_recipe
     ):