[4.2] Limit concurrent-ruby to < 1.3.5

The `concurrent-ruby` gem drops a dependency on the `logger` gem, which
Rails 7.0 implicitly depends on. Rails 7.0 is out of bugfix maintenance,
so we won't see another release that has this bug fixed, so for Solidus
4.2 and 4.1 let's just limit `concurrent-ruby` to versions that *do*
depend on `logger`.

core/solidus_core.gemspec

@@ -35,6 +35,7 @@ Gem::Specification.new do |s|
   s.add_dependency 'awesome_nested_set', '~> 3.3'
   s.add_dependency 'cancancan', ['>= 2.2', '< 4.0']
   s.add_dependency 'carmen', '~> 1.1.0'
+  s.add_dependency 'concurrent-ruby', '< 1.3.5'
   s.add_dependency 'discard', '~> 1.0'
   s.add_dependency 'friendly_id', '~> 5.0'
   s.add_dependency 'image_processing', '~> 1.10'