Why won't Pry run in Heroku's console?

Question

My goal is to use Pry as the console for my Rails app, both locally and on my staging server. But I can't get it to work on Heroku.

I'm following these instructions to get Heroku to use Pry as the console for my Rails app. When I run heroku run console pry, my console prints Running console pry attached to terminal... up, run.1 and then exits. When I run heroku console pry it just says main and then exits.

Any ideas on what I'm doing wrong?

Here's what I've done so far:

1. In my Gemfile I've added the lines:
   gem 'pry'
gem 'pry-rails'

2. I've created a file called pry which contains:
   #!/usr/bin/env ruby
require 'pry'
pry

3. I added the following to all the files in config/environments:
   silence_warnings do
begin
require 'pry'
IRB = Pry
rescue LoadError
end
end

4. run bundle install

5. run git push staging master