Add ostruct to gemspec

[denis-mueller]

Got this warning when starting my rails server

/usr/local/bundle/gems/disposable-0.6.3/lib/disposable/twin/sync.rb:6: warning: /usr/local/lib/ruby/3.3.0/ostruct.rb was loaded from the standard library, but will no longer be part of the default gems starting from Ruby 3.5.0.
You can add ostruct to your Gemfile or gemspec to silence this warning.
Also please contact the author of disposable-0.6.3 to request adding ostruct into its gemspec.

@apotonick

[apotonick]

Haha, what a polite and considerate notification of bundler!

[denis-mueller]

#95 would solve this