LibWeb: Make HTMLSlotElement::assigned_{elements,nodes} methods const

Author: https://github.com/tcl3
Commit: 23473d64ca
Pull-request: https://github.com/SerenityOS/serenity/pull/24207
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/AtkinsSJ
Reviewed-by: https://github.com/shannonbooth ✅

Userland/Libraries/LibWeb/HTML/HTMLSlotElement.cpp

@@ -38,7 +38,7 @@ void HTMLSlotElement::visit_edges(JS::Cell::Visitor& visitor)
 }
 
 // https://html.spec.whatwg.org/multipage/scripting.html#dom-slot-assignednodes
-Vector<JS::Handle<DOM::Node>> HTMLSlotElement::assigned_nodes(AssignedNodesOptions options)
+Vector<JS::Handle<DOM::Node>> HTMLSlotElement::assigned_nodes(AssignedNodesOptions options) const
 {
     // 1. If options["flatten"] is false, then return this's assigned nodes.
     if (!options.flatten) {
@@ -59,7 +59,7 @@ Vector<JS::Handle<DOM::Node>> HTMLSlotElement::assigned_nodes(AssignedNodesOptio
 }
 
 // https://html.spec.whatwg.org/multipage/scripting.html#dom-slot-assignedelements
-Vector<JS::Handle<DOM::Element>> HTMLSlotElement::assigned_elements(AssignedNodesOptions options)
+Vector<JS::Handle<DOM::Element>> HTMLSlotElement::assigned_elements(AssignedNodesOptions options) const
 {
     // 1. If options["flatten"] is false, then return this's assigned nodes, filtered to contain only Element nodes.
     if (!options.flatten) {