[Humble] Add tutorial docker CI job and remove ci-testing job

[sea-bass]

Description

This PR adds the tutorial docker CI job specific to Humble, which was removed from main in #3081.

It also removes the ci-testing Docker build from this branch, since the osrf/ros2:testing image is now on Ubuntu 24.04 and does not have the humble ROS binaries.

Checklist

• Required by CI: Code is auto formatted using clang-format
• Extend the tutorials / documentation reference
• Document API changes relevant to the user in the MIGRATION.md notes
• Create tests, which fail without this PR reference
• Include a screenshot if changing a GUI
• While waiting for someone to review your request, please help review another open pull request to support the maintainers

[mergify]

Please target the main branch for development, we will backport the changes to humble for you if approved and if they don't break API.

[sea-bass]

@sjahr Do you have the powers to remove the "Required" tag from the CI jobs that I've removed here?

Or rather, replace it with the new one?

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.25%. Comparing base (ccf7e5c) to head (2456deb).
Report is 6 commits behind head on humble.

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Additional details and impacted files

@@            Coverage Diff             @@
##           humble    #3082      +/-   ##
==========================================
+ Coverage   51.15%   51.25%   +0.10%     
==========================================
  Files         382      382              
  Lines       31902    31865      -37     
==========================================
+ Hits        16317    16328      +11     
+ Misses      15585    15537      -48     

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[rhaschke]

Just needs adaption of the required CI jobs. Unfortunately, I don't have permissions to change those either.