Auto merge of #12241 - jdm:multiple-stylesheets, r=notriddle

Don't load stylesheets in documents without browsing contexts

Per https://github.com/whatwg/html/issues/1495, this fixes the most commonly reported panic in nightlies by making us match what other browsers do.

---
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #12047 (github issue number if applicable).
- [X] There are tests for these changes OR

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components/script/dom/htmllinkelement.rs

@@ -194,6 +194,10 @@ impl VirtualMethods for HTMLLinkElement {
 impl HTMLLinkElement {
     fn handle_stylesheet_url(&self, href: &str) {
         let document = document_from_node(self);
+        if document.browsing_context().is_none() {
+            return;
+        }
+
         match document.base_url().join(href) {
             Ok(url) => {
                 let element = self.upcast::<Element>();