Use a global bundler cache by default

[deivid-rodriguez]

What was the end-user or developer problem that led to this PR?

What is your fix for the problem, implemented in this PR?

Make sure the following tasks are checked

• Describe the problem / feature
• Write tests for features and bug fixes
• Write code to solve the problem
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[MSP-Greg]

@deivid-rodriguez

I haven't had time to look at the code, and I think this is a good idea. But, is there a way to switch back to the current behavior?

I think this will affect setup-ruby's caching when doing bundle install.

[deivid-rodriguez]

I was not expecting this to cause issues, just maybe the cache to not be hit the first time new bundler runs on an app. But I did not really give this a lot of thought and in particular did not think of ruby/setup-ruby. I will consider it!

[MSP-Greg]

I was working on some other things earlier. I was mistaken, as I don't think this change will affect CI for most users of setup-ruby.

Some CI may run bundle install with different Gemfile files and bundle paths, in which case they may need to download a few more gems, but they could also cache the global bundler cache independent of setup-ruby.

Sorry for the erroneous post...