Fix test infra depending on CI=true

The CI env var was recently [changed][1] to be specific for the
application being tested instead of the framework tests. Because of
this, these lines which should have been true before are now false.

[1]: 1f0262aa2b

activesupport/lib/active_support/testing/strict_warnings.rb

@@ -28,7 +28,7 @@ module ActiveSupport
 
       return unless message.include?(PROJECT_ROOT)
       return if ALLOWED_WARNINGS.match?(message)
-      return unless ENV["RAILS_STRICT_WARNINGS"] || ENV["CI"]
+      return unless ENV["RAILS_STRICT_WARNINGS"] || ENV["BUILDKITE"]
 
       raise message
     end

tools/test_common.rb

@@ -5,9 +5,7 @@ if ENV["BUILDKITE"]
   ENV.delete("CI") # CI has affect on the applications, and we don't want it applied to the apps.
 
   Minitest::Ci.report_dir = File.join(__dir__, "../test-reports/#{ENV['BUILDKITE_JOB_ID']}")
-end
 
-if ENV["CI"]
   module DisableSkipping # :nodoc:
     private
       def skip(message = nil, *)