Add Diego as author of PEP 831 (GH-149551)

(cherry picked from commit 2f6b380)

Co-authored-by: Diego Russo <diego.russo@arm.com>

Author: diegorusso

Doc/whatsnew/3.15.rst

@@ -411,8 +411,8 @@ embedding applications, and native libraries.
    unwinding for the whole Python process.
 
 (Contributed by Pablo Galindo Salgado and Savannah Ostrowski in
-:gh:`149201`; PEP 831 written by Pablo Galindo Salgado, Ken Jin, and
-Savannah Ostrowski.)
+:gh:`149201`; PEP 831 written by Pablo Galindo Salgado, Ken Jin,
+Savannah Ostrowski, and Diego Russo.)
 
 .. seealso:: :pep:`831` for further details.