Improve logging when unable to parse the plugin (backport #285)

[mergify]

I have encountered cases like moveit/moveit2#3599, where invalid XML syntax causes ros2 plugin list to hang and output errors like:

moveit_kinematics:
Traceback (most recent call last):
  File "/opt/ros/rolling/bin/ros2", line 33, in <module>
    sys.exit(load_entry_point('ros2cli==0.40.1', 'console_scripts', 'ros2')())
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/ros/rolling/lib/python3.12/site-packages/ros2cli/cli.py", line 91, in main
    rc = extension.main(parser=parser, args=args)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/ros/rolling/lib/python3.12/site-packages/ros2plugin/command/plugin.py", line 37, in main
    return extension.main(args=args)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/ros/rolling/lib/python3.12/site-packages/ros2plugin/verb/list.py", line 68, in main
    tree = ET.parse(plugin_xml)
           ^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/xml/etree/ElementTree.py", line 1204, in parse
    tree.parse(source, parser)
  File "/usr/lib/python3.12/xml/etree/ElementTree.py", line 569, in parse
    self._root = parser._parse_whole(source)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
xml.etree.ElementTree.ParseError: not well-formed (invalid token): line 2, column 129

This PR makes the error easier to understand and unblock the rest of the packages

Failed to parse plugin XML file: /root/moveit_ws/install/moveit_kinematics/share/moveit_kinematics/cached_ik_kinematics_plugin_description.xml
XML error: not well-formed (invalid token): line 2, column 129
```<hr>This is an automatic backport of pull request #285 done by [Mergify](https://mergify.com).

[ahcorde]

Pulls: #286
Gist: https://gist.githubusercontent.com/ahcorde/28b9478cec7aac3b87f108d3a293a0f3/raw/7611ad9903a560e8b4cdc45db7f7558f632809ef/ros2.repos
BUILD args: --packages-above-and-dependencies ros2plugin
TEST args: --packages-above ros2plugin
ROS Distro: kilted
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/17533

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