dev-cmd/typecheck: Update the Sorbet TODO file in --update-definitions

- [Sorbet's TODO file](https://sorbet.org/docs/rbi#the-todo-rbi-file) is
  useful to be periodically regenerated when we're trying to deal with
  typing errors. The result is an updated `sorbet/rbi/todo.rbi` file that
  defines missing constants. During GSoC, we [did update this file on
  occasional Tapioca updates](https://github.com/Homebrew/brew/blame/master/Library/Homebrew/sorbet/rbi/todo.rbi),
  according to the history. That suggests to me that it should be part of
  this command.

Library/Homebrew/dev-cmd/typecheck.rb

@@ -40,6 +40,7 @@ module Homebrew
       if args.update_definitions?
         system "bundle", "exec", "tapioca", "sync"
         system "bundle", "exec", "srb", "rbi", "hidden-definitions"
+        system "bundle", "exec", "srb", "rbi", "todo"
 
         Homebrew.failed = system("git", "diff", "--stat", "--exit-code") if args.fail_if_not_changed?