Allow Puma 6

Puma 6 was disallowed in 2022, because back then Rails itself generated
Gemfiles with `'puma', "< 6". This is not the case anymore, in fact,
Rails comes with Rack 3 which instead is incompatible with Puma 5.

Author: mamhoff

solidus_dev_support.gemspec

@@ -38,7 +38,7 @@ Gem::Specification.new do |spec|
   spec.add_dependency 'ffaker', '~> 2.13'
   spec.add_dependency 'gem-release', '~> 2.1'
   spec.add_dependency 'github_changelog_generator', '~> 1.15'
-  spec.add_dependency 'puma', '>= 4.3', '< 6.0'
+  spec.add_dependency 'puma', '>= 4.3', '< 7.0'
   spec.add_dependency 'rspec_junit_formatter'
   spec.add_dependency 'rspec-rails', '>= 4.0.0.beta3', '< 6.0'
   spec.add_dependency 'rubocop', '~> 1.0'