fixing doctest syntax

Author: AdityaK1729

src/sage/groups/perm_gps/permgroup.py

@@ -3304,9 +3304,11 @@ def commutator(self, other=None):
             Traceback (most recent call last):
             ...
             TypeError: junk is not a permutation group
-        TESTS ::
+
+        TEST:
             
         Verify that :issue`39416` is fixed::
+
             sage: G = PermutationGroup(gens=[("a", "b"), ("b","c")])
             sage: G.commutator()
             Subgroup generated by [('a','b','c')] of (Permutation Group with generators [('b','c'), ('a','b')])