Declare gnome-shell 40.* compatibility

[roundrobintaborder] / metadata.json

{
  "name": "Round Robin Tab Order",
  "description": "Window switch order becomes round-robin instead of most-recently-used",
  "uuid": "roundrobintaborder@scottworley.com",
  "url": "https://gitlab.gnome.org/chuck/round-robin-tab-order",
  "version": 2,
  "shell-version": [
    "3.32",
    "40"
  ]
}