Add logger dependency to fix Ruby 3.4 warnings

[mattbrictson]

The listen gem depends on logger, but does not properly declare it as a gem dependency. This results in the following warning when using mt --watch on Ruby 3.4:

listen-3.9.0/lib/listen.rb:3: warning: logger was loaded from the standard library, but will no longer be part of the default gems starting from Ruby 3.5.0.
You can add logger to your Gemfile or gemspec to silence this warning.

Since listen does not seem to be actively maintained, I am adding the logger dependency to mighty_test as a workaround.