[FIX] web_editor: prevents dropping a snippet in a non-editable area

Before this commit, it was possible to drop a snippet in a non-editable
area (e.g. dynamic snippets).

Steps to reproduce the bug:

- Drop a "Dynamic Products" snippet in a page.
- Drop a "Columns" snippet in the same page.
- Moves a column from the "Columns" snippet into the "Dynamic Products"
snippet thanks to the "drag and drop" button.
- Bugs => It works when it shouldn't.

task-3054763

closes odoo/odoo#113796

X-original-commit: 4d61c356b7deed7fd0b01cb817c274afe384c0ac
Signed-off-by: Arthur Detroux (ard) <ard@odoo.com>

addons/web_editor/static/src/js/editor/snippets.editor.js

@@ -2327,7 +2327,7 @@ var SnippetsMenu = Widget.extend({
             $selectorSiblings = $(_.uniq(($selectorSiblings || $()).add($selectorChildren.children()).get()));
         }
 
-        var noDropZonesSelector = '[data-invisible="1"], .o_we_no_overlay, :not(:visible)';
+        var noDropZonesSelector = '[data-invisible="1"], .o_we_no_overlay, :not(:visible), :not(:o_editable)';
         if ($selectorSiblings) {
             $selectorSiblings.not(`.oe_drop_zone, .oe_drop_clone, ${noDropZonesSelector}`).each(function () {
                 var data;