Experts list: update David Edelsohn's user name (#1401)

David Edelsohn still wants to be notified of AIX issues, see:
 python/cpython#82809 (comment)

Update to his GitHub username.

Author: encukou

core-developers/experts.rst

@@ -286,7 +286,7 @@ for “their” platform as a third-party project.
 ===================   ===========
 Platform              Maintainers
 ===================   ===========
-AIX                   David.Edelsohn^
+AIX                   edelsohn
 Android               mhsmith
 Cygwin                jlt63^, stutzbach^
 Emscripten            hoodmane, pmp-p, rdb, rth, ryanking13