test both left and right inverse

Co-authored-by: Travis Scrimshaw <clfrngrown@aol.com>

Author: mantepse

src/sage/combinat/partition.py

@@ -2579,6 +2579,7 @@ def glaisher_franklin_inverse(self, s):
         The map is inverse to :meth:`glaisher_franklin`::
 
             sage: all(mu.glaisher_franklin(s).glaisher_franklin_inverse(s) == mu
+            ....:     mu.glaisher_franklin_inverse(s).glaisher_franklin(s) == mu
             ....:     for n in range(20) for mu in Partitions(n)
             ....:     for s in range(1, 5))
             True