Turn extended keys on for tmux

So pi will stop complaining about it and so shift + return will just
work

migrations/1778052575.sh

@@ -0,0 +1,7 @@
+echo "Enable extended keyboard support in tmux"
+
+tmux_config="$HOME/.config/tmux/tmux.conf"
+
+if [[ -f $tmux_config ]] && ! grep -qxF "set -g extended-keys on" "$tmux_config"; then
+  sed -i '/^set -g detach-on-destroy off$/a set -g extended-keys on\nset -g extended-keys-format csi-u\nset -sg escape-time 10' "$tmux_config"
+fi