Migrate CI from Travis to GitHub Actions

[taketo1113]

This Pull Request adds GitHub Actions CI to run tests across multiple Ruby versions.
It also removes the non-functional Travis configuration.

Details

CI Matrix

The GitHub Actions workflow targets Ruby versions from 2.4 through 4.0.
This replaces the existing Travis configuration and adds Ruby 3.0 - 4.0 to the test matrix.

Ruby-Graphviz/.travis.yml

Lines 3 to 8 in 30c0e4d

	rvm:
	- 2.4.9
	- 2.5.7
	- 2.6.5
	- 2.7.0
	- jruby-9.2.9.0

• Close Enable bundler caching for travis #150

Remove github_changelog_generator development dependency on JRuby

Bundler fails on JRuby due to dependency issues in github_changelog_generator.
To avoid this, this PR removes github_changelog_generator as a development dependency when running on JRuby.

Example error:

$ /home/runner/.rubies/jruby-9.4.14.0/bin/bundle install --jobs 4
...
An error occurred while installing io-event (1.11.2), and Bundler cannot
continue.

In Gemfile:
  github_changelog_generator was resolved to 1.16.4, which depends on
    async-http-faraday was resolved to 0.22.0, which depends on
      async-http was resolved to 0.88.0, which depends on
        async-pool was resolved to 0.10.3, which depends on
          async was resolved to 2.24.0, which depends on
            io-event
Error: The process '/home/runner/.rubies/jruby-9.4.14.0/bin/bundle' failed with exit code 5