upgrade webkit (#13192)

Co-authored-by: Dylan Conway <dylan.conway567@gmail.com>
Co-authored-by: Zack Radisic <zack@theradisic.com>

src/string.zig

@@ -645,7 +645,7 @@ pub const String = extern struct {
     /// Max WTFStringImpl length.
     /// **Not** in bytes. In characters.
     pub inline fn max_length() usize {
-        return JSC.synthetic_allocation_limit;
+        return JSC.string_allocation_limit;
     }
 
     /// If the allocation fails, this will free the bytes and return a dead string.