Add Ruby 3.3 to CI

[imjoehaines]

Goal

Add Ruby 3.3 to CI

Changeset

• assert against in-project frames in the plain ruby unhandled error tests — Ruby 3.3 adds additional frames to the top of these stacktraces
• update "undefined local variable" message assertions:
  • Ruby <3.3:

    undefined local variable or method `generate_unhandled_error' for #\

  • Ruby 3.3:

    undefined local variable or method `generate_unhandled_error' for an instance of BeforeNotifyController

• add Ruby 3.3 to matrices
• fix dependency issue in the Rails 7 fixture when running with Ruby 2.7