Fix func_persist: do not use the (now removed) inspect.formatargspec,

but instead use inspect.signature.

src/sage/misc/func_persist.py

@@ -45,7 +45,6 @@ def bern(n):
 
 from . import persist
 
-
 class func_persist:
     r"""
     Put ``@func_persist`` right before your function
@@ -57,7 +56,7 @@ def __init__(self, f, dir='func_persist'):
         os.makedirs(dir, exist_ok=True)
         self.__doc__ = '%s%s%s' % (
             f.__name__,
-            inspect.formatargspec(*inspect.getargs(f.__code__)),
+            inspect.signature(f),
             f.__doc__)
 
     def __call__(self, *args, **kwds):