Set a default type="button" for JS buttons

> The `button` [type] has no default behavior, and does nothing when pressed by default. It can have client-side scripts listen to the element's events, which are triggered when the events occur. — https://developer.mozilla.org/en-US/docs/Web/HTML/Element/button

umap/static/umap/js/umap.core.js

@@ -318,6 +318,7 @@ L.DomUtil.createButton = (className, container, content, callback, context) => {
   const el = L.DomUtil.add('a', className, container, content)
   el.href = '#'
   // const el = L.DomUtil.add('button', className, container, content)
+  // el.type = 'button'
   if (callback) {
     L.DomEvent.on(el, 'click', L.DomEvent.stop).on(el, 'click', callback, context)
   }