Update puppet_litmus requirement from ~> 1.0 to ~> 2.0

Updates the requirements on [puppet_litmus](https://github.com/puppetlabs/puppet_litmus) to permit the latest version.
- [Release notes](https://github.com/puppetlabs/puppet_litmus/releases)
- [Changelog](https://github.com/puppetlabs/puppet_litmus/blob/main/CHANGELOG.md)
- [Commits](puppetlabs/puppet_litmus@v1.0.0...v2.0.0)

---
updated-dependencies:
- dependency-name: puppet_litmus
  dependency-version: 2.0.0
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Gemfile

@@ -36,7 +36,7 @@ group :development, :release_prep do
   gem "puppetlabs_spec_helper", '~> 8.0', require: false
 end
 group :system_tests do
-  gem "puppet_litmus", '~> 1.0',   require: false, platforms: [:ruby, :x64_mingw]
+  gem "puppet_litmus", '~> 2.0',   require: false, platforms: [:ruby, :x64_mingw]
   gem "CFPropertyList", '< 3.0.7', require: false, platforms: [:mswin, :mingw, :x64_mingw]
   gem "serverspec", '~> 2.41',     require: false
 end