LibJS: Mark [[HostDefined]] accessor on scripts as const

Author: https://github.com/networkException
Commit: 5a3e079deb
Pull-request: https://github.com/SerenityOS/serenity/pull/15275
Reviewed-by: https://github.com/davidot ✅
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibJS/Script.h

@@ -32,7 +32,7 @@ public:
     Realm& realm() { return *m_realm; }
     Program const& parse_node() const { return *m_parse_node; }
 
-    HostDefined* host_defined() { return m_host_defined; }
+    HostDefined* host_defined() const { return m_host_defined; }
     StringView filename() const { return m_filename; }
 
 private: