Ruby 3.2.0 compatibility

[henrycatalinismith]

First error is from the old version of Rugged.

Provided configuration options:
    --with-opt-dir
    --without-opt-dir
    --with-opt-include
    --without-opt-include=${opt-dir}/include
    --with-opt-lib
    --without-opt-lib=${opt-dir}/lib
    --with-make-prog
    --without-make-prog
    --srcdir=.
    --curdir
    --ruby=/opt/hostedtoolcache/Ruby/3.2.0/x64/bin/$(RUBY_BASE_NAME)
    --with-sha1dc
    --without-sha1dc
    --use-system-libraries
extconf.rb:101:in `block in <main>': undefined method `exists?' for Dir:Class
(NoMethodError)
    Dir.mkdir("build") if !Dir.exists?("build")
                              ^^^^^^^^
Did you mean?  exist?
    from extconf.rb:100:in `chdir'
    from extconf.rb:100:in `<main>'
To see why this extension failed to compile, please check the mkmf.log which can
be found here:
/opt/hostedtoolcache/Ruby/3.2.0/x64/lib/ruby/gems/3.2.0/extensions/x86_64-linux/3.2.0/rugged-1.1.0/mkmf.log

Fixed by 08fe54d.

[henrycatalinismith]

Next error

An error occurred while loading spec_helper. - Did you mean?
                    rspec ./spec/spec_helper.rb
Failure/Error: require "mail"
LoadError:
  cannot load such file -- net/smtp

[henrycatalinismith]

Fixed in ae9d3cc. Context in https://github.com/mikel/mail/issues/1461.