gh-35521: sage.combinat.sf: re-enable a doctest

    
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Rebased an ancient ticket branch from @darijgr:
- Fixes #15475
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URL: #35521
Reported by: Matthias Köppe
Reviewer(s): Frédéric Chapoton

src/sage/combinat/sf/sfa.py

@@ -403,10 +403,8 @@ def is_integral_domain(self, proof=True):
                 sage: s.is_integral_domain()
                 True
 
-            The following doctest is disabled pending :trac:`15475`::
-
-                sage: s = SymmetricFunctions(Zmod(14)).s() # not tested
-                sage: s.is_integral_domain() # not tested
+                sage: s = SymmetricFunctions(Zmod(14)).s()
+                sage: s.is_integral_domain()
                 False
             """
             return self.base_ring().is_integral_domain()