gh-40462: fix a doctest error in src/sage/interfaces/polymake.py
    
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Fixes #40461, Fixes an doctest error in  polymake.py


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URL: #40462
Reported by: Chenxin Zhong
Reviewer(s): Chenxin Zhong, Frédéric Chapoton

Author: Release Manager

src/sage/interfaces/polymake.py

@@ -446,6 +446,7 @@ def clear(self, var):
         TESTS::
 
             sage: # optional - jupymake
+            sage: from sage.interfaces.polymake import polymake
             sage: c = polymake.cube(15)
             sage: polymake._available_vars = []
             sage: old = c._name