Trac #34465: Invalid escape sequence in special.py

I just saw this when doctesting:
{{{
/Users/jpalmier/Desktop/Sage/git/sage/src/sage/functions/special.py:852:
DeprecationWarning: invalid escape sequence '\p'
}}}
To reproduce: assuming you have an editable build, run `touch
src/sage/functions/special.py` and then doctest a file.

URL: https://trac.sagemath.org/34465
Reported by: jhpalmieri
Ticket author(s): John Palmieri
Reviewer(s): Dima Pasechnik

Author: Release Manager

src/sage/functions/special.py

@@ -849,7 +849,7 @@ class EllipticF(BuiltinFunction):
     - :wikipedia:`Elliptic_integral#Incomplete_elliptic_integral_of_the_first_kind`
     """
     def __init__(self):
-        """
+        r"""
         EXAMPLES::
 
             sage: loads(dumps(elliptic_f))