Do not report examples as non-list elements

[jhradilek]

In a generated tasks, if an example block directly follows the procedure, the dita-convert utility incorrectly issues the following warning despite not skipping any content:

file.dita: WARNING: Non-list elements found in steps, skipping...

This pull request fixes this issue and also corrects the tests to correctly count expected error and warning messages.

Example AsciiDoc code

:_mod-docs-content-type: PROCEDURE

[#task-id]
= Task title

.Procedure
. A step.

.Example title
====
An example.
====

Implementation checklist

• The code changes come with the corresponding test cases
• The code changes pass all tests (run python3 -m unittest in the project directory)
• The code changes come with appropriate documentation