Adding Test::Mojo::message_* tests.

[sergiotarxz]

Summary

Adding tests for the Test::Mojo::message_* methods.

Motivation

Issue #1488.

References

#1488

[sergiotarxz]

I think it is not my fault these two test fail:

@github-actions
linux / perl (5.22) (pull_request) Failing after 2m
Required
[Details](https://github.com/mojolicious/mojo/actions/runs/7862274388/job/21451556660?pr=2153)
@github-actions
linux / perl (5.30) (pull_request) Failing after 2m

I think it failed to download extutils::makemaker.