Bump stable to 31.0.4

Signed-off-by: J0WI <J0WI@users.noreply.github.com>

generate-stackbrew-library.sh

 #!/usr/bin/env bash
 set -Eeuo pipefail
 
-stable_channel='30.0.9'
+stable_channel='31.0.4'
 
 self="$(basename "$BASH_SOURCE")"
 cd "$(dirname "$(readlink -f "$BASH_SOURCE")")"