sorbet/homebrew.rbi: solve fetch.rb type error

Latest changes to fetch.rb introduced 2 new type errors.
These changes in sorbet/rbi/homebrew.rbi resolves those errors.

Library/Homebrew/sorbet/rbi/homebrew.rbi

@@ -8,6 +8,10 @@ module Homebrew::Help
   include Kernel
 end
 
+module Homebrew::Fetch
+  def args; end
+end
+
 module Language::Perl::Shebang
   include Kernel
 end