Log that prepared_statements enabled for mysql2

Enabling this flag locally prevents the test schema from loading with
mysql2, so this commit tests my theory that the ENV var is not making it
to the CI job.

Author: skipkayhil

activerecord/test/support/connection.rb

@@ -20,7 +20,7 @@ def self.test_configuration_hashes
 
   def self.connect
     ActiveRecord.async_query_executor = :global_thread_pool
-    puts "Using #{connection_name}"
+    puts "Using #{connection_name}#{ " with prepared statements" if ENV["MYSQL_PREPARED_STATEMENTS"]}"
 
     if ENV["BUILDKITE"]
       ActiveRecord::Base.logger = nil