fix: do not try to animate the panel

The panel inherits from the classic Popup, but given it's fixed on
the UI, it does not make sense to try to move it, and it some
situation there is a race condition that make Leaflet try to animate
but this fails

umap/static/umap/js/umap.popup.js

@@ -96,6 +96,7 @@ U.Popup.Panel = U.Popup.extend({
   _updateLayout: function () {},
   _updatePosition: function () {},
   _adjustPan: function () {},
+  _animateZoom: function () {},
 })
 U.Popup.SimplePanel = U.Popup.Panel // Retrocompat.