Don't mpmath.ctx_mp_python.mpf, but mpmath.mpf

See https://groups.google.com/g/mpmath/c/qzA5gs57Qm8/m/sksRJOGrAAAJ

Author: rocky

mathics/builtin/constants.py

@@ -23,7 +23,7 @@
 from mathics.core.numbers import get_precision, PrecisionValueError, machine_precision
 
 
-def mp_constant(fn: str, d=None) -> mpmath.ctx_mp_python.mpf:
+def mp_constant(fn: str, d=None) -> mpmath.mpf:
     """
     Return the mpmath constant _fn_ with integer precision _d_.
     """