bpo-35044, doc: Use the :exc: role for the exceptions (GH-10037)

(cherry picked from commit e483f02423917dc4dfd25f46e5b9e6fce304777d)

Co-authored-by: Stéphane Wirtel <stephane@wirtel.be>
diff --git a/Doc/c-api/conversion.rst b/Doc/c-api/conversion.rst
index 9566d9d..c46722d 100644
--- a/Doc/c-api/conversion.rst
+++ b/Doc/c-api/conversion.rst
@@ -60,7 +60,7 @@
    The conversion is independent of the current locale.
 
    If ``endptr`` is ``NULL``, convert the whole string.  Raise
-   ValueError and return ``-1.0`` if the string is not a valid
+   :exc:`ValueError` and return ``-1.0`` if the string is not a valid
    representation of a floating-point number.
 
    If endptr is not ``NULL``, convert as much of the string as