BUG: fix isalpha docstring undetermined string literal

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Author: luxedo

numpy/_core/code_generators/ufunc_docstrings.py

@@ -4377,7 +4377,7 @@ def add_newdoc(place, name, doc):
     --------
     >>> np.char.isalpha(["yes", "alpha"])
     array([ True,  True])
-    >>> np.char.isalpha(["not", "\x00", "alpha"])
+    >>> np.char.isalpha(["not", "\\x00", "alpha"])
     array([ True, False,  True])
     >>> np.char.isalpha(["n0t", "4lpha"])
     array([ False, False])