Supress frozen middleware errors in Railtie
Supress frozen middleware errors in Railtie

This should never happen in normal operation, but is possible when
running RSpec tests

See https://github.com/thoughtbot/factory_bot_rails/issues/303#issuecomment-434560625
and https://github.com/bugsnag/bugsnag-ruby/issues/534

Essentially this happens:
1. RSpec boots Rails
2. Rails boot process errors
3. Rails freezes middleware
4. RSpec moves on to the next test file
5. Bugsnag tries to add middleware but fails because it's frozen
6. The stacktrace blames Bugsnag for this test failure
7. goto 4

Supressing this error doesn't solve the problem as it's likely another
frozen error will happen in some other library/component, but we want
to avoid people thinking this is caused by Bugsnag. The stacktrace
does point out the actual problem, but only in the very first error,
which can get buried under the frozen errors that happen for each
test file

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