Drop Ruby < 3.0 support

[AlexWayfer]

Basic Info

• Faraday Version: 2.8.1
• Ruby Version: 2.7.8

Issue description

1. Ruby <= 2.7 is no longer supported, even with security patches.
2. Now simple standard gem update --system or gem install bundler are broken, but I believe there no reason to report about this, because, as I've already wrote, it's no longer supported.

Steps to reproduce

1. Install Ruby 2.7.8.
2. Run gem update --system or gem install bundler.

Details

> gem update --system
Updating rubygems-update
Fetching rubygems-update-3.5.3.gem
ERROR:  Error installing rubygems-update:
	There are no versions of rubygems-update (= 3.5.3) compatible with your Ruby & RubyGems
	rubygems-update requires Ruby version >= 3.0.0. The current ruby version is 2.7.8.225.
ERROR:  While executing gem ... (NoMethodError)
    undefined method `version' for nil:NilClass

https://cirrus-ci.com/task/4917812326563840?logs=install#L0

> gem install bundler
ERROR:  Error installing bundler:
	The last version of bundler (>= 0) to support your Ruby & RubyGems was 2.4.22. Try installing it with `gem install bundler -v 2.4.22`
	bundler requires Ruby version >= 3.0.0. The current ruby version is 2.7.8.225.

https://cirrus-ci.com/task/6537682302533632?logs=install#L0

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What do you think? Do you really still want to continue to support such old Ruby versions?

[AlexWayfer]

Probably it should be a discussion. 🤔 Sorry, I'm still not familiar with this separation, you're free to move/convert.