shopify-scripts: mrb_str_modify try to write to memory not marked for writing

The proof-of-concept below can be used to crash the interpreter DoS because forces it to try to write a memory not marked for writing. a = Time.new.zone a.rstrip! GC.start a.next! Code https://github.com/mruby/mruby/blob/5289b4ba117e66bdef1438ca754c894508a2447b/src/string.cL668 if shared-refcnt =...