Suppress output from mail parser warnings

Previously, requiring any of the ragel generated parsers in mail would
output tons of warnings in tests, making output much harder to read
(especially in Railties).

This commit extends the RaiseWarnings patch to suppress output from
these mail parsers.

The suppression can be removed once mikel/mail#1557 or mikel/mail#1551
or any other PR fixes the issue

activesupport/lib/active_support/testing/strict_warnings.rb

@@ -12,7 +12,16 @@ module RaiseWarnings
     /Ignoring .*\.yml because it has expired/,
     /Failed to validate the schema cache because/,
   )
+
+  SUPPRESSED_WARNINGS = Regexp.union(
+    # TODO: remove if https://github.com/mikel/mail/pull/1557 or similar fix
+    %r{/lib/mail/parsers/.*statement not reached},
+    %r{/lib/mail/parsers/.*assigned but unused variable - testEof}
+  )
+
   def warn(message, *)
+    return if SUPPRESSED_WARNINGS.match?(message)
+
     super
 
     return unless message.include?(PROJECT_ROOT)