Be explicit about can_submit_spot methods

providers/spot/xota.py

@@ -58,3 +58,9 @@ class XOTA(WebsocketSpotProvider):
             qrt=source_spot["state"] != "active",
         )
         return spot
+
+    # I haven't investigated whether xOTA has a spot submission API, but as we only use it for
+    # Toilets on the air currently, and realistically no-one is entering their Toilet spots using
+    # Spothole, this is very low priority.
+    def can_submit_spot(self, activity):
+        return False