update package.py: unique python_classifiers

Author: yuji38kwmt

src/poetry/core/packages/package.py

@@ -348,7 +348,7 @@ def all_classifiers(self) -> list[str]:
         # it like this so that 3.10 is sorted after 3.9.
         sorted_classifiers = []
         python_classifiers_inserted = False
-        for classifier in sorted(set(classifiers)):
+        for classifier in sorted(set(classifiers) - set(python_classifiers)):
             if (
                 not python_classifiers_inserted
                 and classifier > python_classifier_prefix