Deprecation warnings should be silenced in testing

[jamiemccarthy]

The test suite for ActiveRecord 5.x emits deprecation warnings. They don't break anything but they are ugly and may confuse people reading the test suite output into thinking there is something wrong. Since these warnings are expected, they should be silenced.

There are two:

1. SQLite 1.3 warning of incompatibility with Ruby 3.2 (which is irrelevant since Rails 5 won't run on Ruby 3.2 and Rails 6 requires SQLite 1.4).
2. DEPRECATION WARNING: Leaving ActiveRecord::ConnectionAdapters::SQLite3Adapter.represent_boolean_as_integer set to false is deprecated.

[jamiemccarthy]

Technically there's a third, but it's similar to the first:

/usr/local/bundle/gems/activerecord-5.2.8.1/lib/active_record/connection_adapters/sqlite3_adapter.rb:32: warning: rb_check_safe_obj will be removed in Ruby 3.0