Ignore browser generated invalid mime types

Rails 6.0 started raising an error when parsing invalid mime types but
this was a generic error so couldn't be globally ignored. In #40353 this
was changed to a more specific error that refers only to browsers sending
invalid `Accept` headers in the request so add that to the ignored list.

config/appsignal.yml

@@ -21,6 +21,7 @@ default: &defaults
   # Exceptions that should not be recorded by AppSignal
   ignore_errors:
     - ActionDispatch::ParamsParser::ParseError
+    - ActionDispatch::Http::MimeNegotiation::InvalidType
     - ActionController::BadRequest
     - ActionController::InvalidAuthenticityToken
     - ActionController::RoutingError