Avoid collecting scoped import for "Literal"

`py_import` can already be imported manually in the module's namespace.
In which case `py_import` cannot be formatted as an import and shouldn't
be collected.

Author: lagru

src/docstub/_docstrings.py

@@ -395,7 +395,7 @@ def natlang_literal(self, tree):
 
         if self.matcher is not None:
             _, py_import = self.matcher.match("Literal")
-            if py_import:
+            if py_import.has_import:
                 self._collected_imports.add(py_import)
         return out