util: Handle .rc in version comparisons

We somehow missed that the new version scheme include '.rc' when
adding the comparison function, whoops.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3130>

js/misc/util.js

@@ -294,8 +294,10 @@ function _GNOMEversionToNumber(version) {
     if (!isNaN(ret))
         return ret;
     if (version === 'alpha')
-        return -2;
+        return -3;
     if (version === 'beta')
+        return -2;
+    if (version === 'rc')
         return -1;
     return ret;
 }