Test: filter out warnings from the mail gem

[olleolleolle]

These warnings are not relevant to the output, but dominate it.

I borrowed the Warning example from the Ruby documentation.

[fatkodima]

Seems like mail gem will never fix these warnings. 🙄

[olleolleolle]

@fatkodima Nice improvements!

Now, there are more output lines than warning lines, at least.

Run bundle exec rake test
/home/runner/work/data_checks/data_checks/vendor/bundle/ruby/3.2.0/gems/mail-2.8.1/lib/mail/parsers/date_time_parser.rb:837: warning: statement not reached
/home/runner/work/data_checks/data_checks/vendor/bundle/ruby/3.2.0/gems/mail-2.8.1/lib/mail/parsers/date_time_parser.rb:691: warning: assigned but unused variable - testEof
Run options: --seed 14750

# Running:

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Finished in 0.408193s, 149.4390 runs/s, 489.9640 assertions/s.
61 runs, 200 assertions, 0 failures, 0 errors, 0 skips