Re-add ruby head to ci (#2631)

Author: solnic

.github/workflows/sentry_ruby_test.yml

@@ -53,7 +53,6 @@ jobs:
             rack_version: 3.1
             redis_rb_version: 5.3
         exclude:
-          - ruby_version: 'head' # all rack versions are broken now under head
           - ruby_version: 'jruby'
           - ruby_version: 'jruby-head'
     steps:

Gemfile

@@ -15,6 +15,10 @@ if ruby_version >= Gem::Version.new("2.7.0")
   gem "ruby-lsp-rspec" if ruby_version >= Gem::Version.new("3.0.0") && RUBY_PLATFORM != "java"
 end
 
+if RUBY_VERSION >= "3.5"
+  gem "cgi"
+end
+
 # For RSpec
 gem "rspec", "~> 3.0"
 gem "rspec-retry"