Add ruby@4.0 to the CI matrix

[seanpdoyle]

According to Ruby 4.0's Release Notes, the stdlib no longer includes the CGI library by default. This means that CGI.parse is no longer available without explicitly requiring the cgi gem as a dependency.

To uncover this requirement, add 4.0 to the ruby matrix in the GitHub actions configuration file, then add cgi as a dependency to the gemspec.

Without explicit access, attempts to OAuth fail with an error message including:

undefined method 'parse' for class CGI: NoMethodError, undefined method 'parse' for class CGI

[seanpdoyle]

@arunagw I may need some assistance in getting CI to bundle install properly:

https://github.com/arunagw/omniauth-twitter/actions/runs/21002962530/job/60421304927?pr=153#step:3:39

> bundle install
Setting BUNDLER_VERSION=4 for "bundle config|lock" commands below to ensure Bundler 4 is used
/opt/hostedtoolcache/Ruby/4.0.1/x64/bin/bundle config set --local path /home/runner/work/omniauth-twitter/omniauth-twitter/vendor/bundle
/opt/hostedtoolcache/Ruby/4.0.1/x64/bin/bundle lock
Writing lockfile to /home/runner/work/omniauth-twitter/omniauth-twitter/Gemfile.lock
Fetching gem metadata from https://rubygems.org/...........
Resolving dependencies...
Could not find compatible versions

Because the current Bundler version (4.0.3) does not satisfy bundler ~> 2.0
  and Gemfile depends on bundler ~> 2.0,
  version solving has failed.

Your bundle requires a different version of Bundler than the one you're running.
Install the necessary version with `gem install bundler:2.7.2` and rerun bundler
using `bundle _2.7.2_ lock`

Is that something you're familiar with troubleshooting?

[raysrashmi]

@seanpdoyle Removed the bundler dependency in this PR #155 .
please rebase master

[seanpdoyle]

@raysrashmi thank you for the help! This is rebased and ready for CI to execute.