`tapioca gem` crashes if you have an RBS sig on `method_added` or `singleton_method_added`

[amomchilov]

If you run tapioca gem on a repo that has an RBS signature on one of these two methods, Tapioca crashes with:

There was an error while trying to load the gem 'your_gem'. (Bundler::GemRequireError)
Gem Load Error is: Putting a sig on method_added is not supported (sorbet-runtime uses this method internally to perform sig validation logic)

Caused by Spoom issue. Just documenting here for search-ability.