chore: Constrain activesupport < 7.2 for Grape 1.8.0 compatibility

Grape 1.8.0 is incompatible with activesupport >= 7.2 due to deprecation API
changes. Add conditional constraint to allow testing with Grape 1.8.0 while
maintaining compatibility with Grape 2.x and 3.x.

Author: numbata

Gemfile

@@ -24,6 +24,7 @@ group :development, :test do
   if grape_version == 'HEAD' || Gem::Version.new(grape_version) >= Gem::Version.new('2.0.0')
     gem 'rack', '>= 3.0'
   else
+    gem 'activesupport', '< 7.2'
     gem 'rack', '< 3.0'
   end