Allow rspec-rails 6

rspec-rails < 6.0.2 is incompatible with Rails 7.1 because of stricter
view path typecasting in Rails 7.1. This bug is fixed in rspec-rails
6.0.2. Without this, controller specs in extensions will break.

rspec/rspec-rails#2631

This also raises the minimum version to rspec-rails 5 as Solidus 3.x
needs Rails > 5.2, and rspec-rails 5 is the version for that Rails
version.

solidus_dev_support.gemspec

@@ -40,7 +40,7 @@ Gem::Specification.new do |spec|
   spec.add_dependency 'github_changelog_generator', '~> 1.15'
   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 'rspec-rails', '>= 5.0', '< 7.0'
   spec.add_dependency 'rubocop', '~> 1.0'
   spec.add_dependency 'rubocop-performance', '~> 1.5'
   spec.add_dependency 'rubocop-rails', '~> 2.3'