Add rexml dependency

[znz]

Description

Since ruby 3.0.0, rexml is a bundled gem.
So it must be depend explicitly.

Motivation and Context

https://stackoverflow.com/questions/65479863/rails-6-1-what-is-preventing-tests-from-running/65480744#65480744

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the contributing document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

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All committers have signed the CLA.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!

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[titusfortner]

Since Selenium 4 has removed the Firefox extension, I think the right answer for trunk is to delete the requires from firefox.rb rather than adding the dependency. I haven't had a chance to pull Ruby 3 yet to check it out, yet...

[voxik]

There are also other places with REXML:

selenium/rb/lib/selenium/server.rb

Lines 112 to 121 in 109c25a

	def latest
	require 'rexml/document'
	net_http_start('selenium-release.storage.googleapis.com') do |http|
	versions = REXML::Document.new(http.get('/').body).root.get_elements('//Contents/Key').map do |e|
	e.text[/selenium-server-standalone-(\d+\.\d+\.\d+)\.jar/, 1]
	end
	versions.compact.map { |version| Gem::Version.new(version) }.max.version
	end
	end

[ioquatix]

Also have this problem, fixed it by adding gem 'rexml' to my own gemfile, but good to see it's merged here. What's the ETA on the 4.0 release?

[titusfortner]

@ioquatix go ahead and use the beta. Very little will change in Ruby bindings between now and final release.