[3.14] Replace `capi-sig` mailing list with `discuss.python.org` (GH-136211) (#136213)

Replace `capi-sig` mailing list with `discuss.python.org` (GH-136211)
(cherry picked from commit 7afe1adb0089d0f2df2add79bbc2300c2f236d90)

Co-authored-by: sobolevn <[email protected]>
1 file changed