LibWeb: Port CSSStyleSheet interface from DeprecatedString to String

Author: https://github.com/shannonbooth
Commit: da637a527d
Pull-request: https://github.com/SerenityOS/serenity/pull/20926
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/trflynn89 ✅

Userland/Libraries/LibWeb/CSS/CSSStyleSheet.h

@@ -29,7 +29,7 @@ public:
 
     void set_owner_css_rule(CSSRule* rule) { m_owner_css_rule = rule; }
 
-    virtual DeprecatedString type() const override { return "text/css"; }
+    virtual String type() const override { return "text/css"_string; }
 
     CSSRuleList const& rules() const { return *m_rules; }
     CSSRuleList& rules() { return *m_rules; }