Fix plugin loading in gazebo (backport #876)

[mergify]

Description

Fix plugin loading in gazebo in non-standard environments such as pixi/conda

Fixes: #877

Is this user-facing behavior change?

Did you use Generative AI?

Additional Information

Similar to: https://github.com/gazebosim/ros_gz/blob/jazzy/ros_gz_sim_demos/hooks/ros_gz_sim_demos.dsv.in

TODOs

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This is an automatic backport of pull request #876 done by [Mergify](https://mergify.com).

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