Replace allow(crown::unrooted_must_root) with expect(crown::unrooted_must_root) (#41815)

Testing: `./mach build -d --use-crown` with no warnings
Fixes: #41761

Signed-off-by: WaterWhisperer <waterwhisperer24@qq.com>

components/script/dom/css/cssrule.rs

@@ -40,7 +40,6 @@ pub(crate) struct CSSRule {
 }
 
 impl CSSRule {
-    #[cfg_attr(crown, allow(crown::unrooted_must_root))]
     pub(crate) fn new_inherited(parent_stylesheet: &CSSStyleSheet) -> CSSRule {
         CSSRule {
             reflector_: Reflector::new(),