Move comment to the right code line in code-block (backport #5400)

[mergify]

Follow-up to #5322, see #5322 (comment)

This was originally:

.. code-block:: console

    # Make a virtual env and activate it
    virtualenv -p python3 ./venv
    source ./venv/bin/activate
    # Make sure that colcon does not try to build the venv
    touch ./venv/COLCON_IGNORE

So the second comment belongs to the last line, not the second line.

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This is an automatic backport of pull request #5400 done by Mergify.

[github-actions]

HTML artifacts: https://github.com/ros2/ros2_documentation/actions/runs/14717354631/artifacts/3025131307.

To view the resulting site:

1. Click on the above link to download the artifacts archive
2. Extract it
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