Restrict Postgres image to v13
Restrict Postgres image to v13

v14 causes issues on older Rubies and there doesn't seem to be a
combination of dependencies that are compatible with Ruby 2.0-2.3
AND Postgres 14

bugsnag/bugsnag-ruby,bugsnag/bugsnag-ruby,bugsnag/bugsnag-ruby,bugsnag/bugsnag-ruby