#39266: fix default parameter in DeBruijn

Author: dcoudert

src/sage/graphs/digraph_generators.py

@@ -950,7 +950,7 @@ def Circulant(self, n, integers):
 
         return G
 
-    def DeBruijn(self, k, n, vertices='strings', immutable=True):
+    def DeBruijn(self, k, n, vertices='strings', immutable=False):
         r"""
         Return the De Bruijn digraph with parameters `k,n`.