Add Ruby 2.7-3.4 to the CI matrix

[taketo1113]

This Pull Request adds Ruby 2.7-3.4 to the CI matrix.

Changes

Update the CI matrix

• Added Ruby 2.7-3.4 to the CI matrix.
• Removed the patch version numbers from the version format to ensure that the latest patch version of each Ruby version is used.

Relax version constraints for 'mocha' and 'minitest' for development dependencies.

This addresses the following error occurred with Ruby 3.4 and minitest v5.2.0:

/bundle_path/ruby/3.4.0/gems/minitest-5.2.0/lib/minitest.rb:3: warning: mutex_m was loaded from the standard library, but is not part of the default gems starting from Ruby 3.4.0.
You can add mutex_m to your Gemfile or gemspec to silence this warning.
/Users/taketo/.rbenv/versions/3.4.2/lib/ruby/3.4.0/bundled_gems.rb:82:in 'Kernel.require': cannot load such file -- mutex_m (LoadError)

Fix incorrect casing of 'Minitest' in test case definition.

At least as of minitest v5.2.0, the class name is Minitest, so I have updated it to match the actual class name.

https://github.com/minitest/minitest/blob/v5.2.0/lib/minitest/test.rb#L3

This fixes the following NameError that occurred with Ruby 3.4.

/path/whenever/test/test_case.rb:8:in '<module:Whenever>': uninitialized constant Whenever::MiniTest (NameError)

    class TestCase < MiniTest::Unit::TestCase; end
                     ^^^^^^^^
Did you mean?  Minitest
	from /path/whenever/test/test_case.rb:1:in '<top (required)>'
	from /Users/taketo/.rbenv/versions/3.4.2/lib/ruby/3.4.0/bundled_gems.rb:82:in 'Kernel.require'
	from /Users/taketo/.rbenv/versions/3.4.2/lib/ruby/3.4.0/bundled_gems.rb:82:in 'block (2 levels) in Kernel#replace_require'
	from /path/whenever/test/test_helper.rb:2:in '<top (required)>'
	from /Users/taketo/.rbenv/versions/3.4.2/lib/ruby/3.4.0/bundled_gems.rb:82:in 'Kernel.require'
	from /Users/taketo/.rbenv/versions/3.4.2/lib/ruby/3.4.0/bundled_gems.rb:82:in 'block (2 levels) in Kernel#replace_require'
	from /path/whenever/test/functional/command_line_test.rb:1:in '<top (required)>'
	from /Users/taketo/.rbenv/versions/3.4.2/lib/ruby/3.4.0/bundled_gems.rb:82:in 'Kernel.require'
	from /Users/taketo/.rbenv/versions/3.4.2/lib/ruby/3.4.0/bundled_gems.rb:82:in 'block (2 levels) in Kernel#replace_require'
	from /path/whenever/tmp/ruby/3.4.0/gems/rake-13.2.1/lib/rake/rake_test_loader.rb:21:in 'block in <main>'
	from /path/whenever/tmp/ruby/3.4.0/gems/rake-13.2.1/lib/rake/rake_test_loader.rb:6:in 'Array#select'
	from /path/whenever/tmp/ruby/3.4.0/gems/rake-13.2.1/lib/rake/rake_test_loader.rb:6:in '<main>'

Use 'mocha/minitest' instead of 'mocha/setup'

This addresses the following deprecation warning:

Mocha deprecation warning at /Users/taketo/.rbenv/versions/3.4.2/lib/ruby/3.4.0/bundled_gems.rb:82:in 'Kernel.require': Require 'mocha/test_unit', 'mocha/minitest' or 'mocha/api' instead of 'mocha/setup'.