build(deps): bump sortablejs from 1.15.2 to 1.15.6

Bumps [sortablejs](https://github.com/SortableJS/Sortable) from 1.15.2 to 1.15.6.
- [Release notes](https://github.com/SortableJS/Sortable/releases)
- [Commits](https://github.com/SortableJS/Sortable/compare/1.15.2...1.15.6)

---
updated-dependencies:
- dependency-name: sortablejs
  dependency-version: 1.15.6
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

package.json

@@ -114,7 +114,7 @@
 		"prosemirror-view": "^1.34.3",
 		"pyodide": "^0.27.3",
 		"socket.io-client": "^4.2.0",
-		"sortablejs": "^1.15.2",
+		"sortablejs": "^1.15.6",
 		"svelte-sonner": "^0.3.19",
 		"tippy.js": "^6.3.7",
 		"turndown": "^7.2.0",