tools: fix XDG desktop syntax in gnome-shell-overrides-migration
Reported by desktop-file-validate: error: value "True" for boolean key "NoDisplay" in group "Desktop Entry" contains invalid characters, boolean values must be "false" or "true"
Reported by desktop-file-validate: error: value "True" for boolean key "NoDisplay" in group "Desktop Entry" contains invalid characters, boolean values must be "false" or "true"