prevent AttributeError when static_only=true (backport #906)

[mergify]

Description

preventing AttributeError when the listener was created with static_only=True

Did you use Generative AI?

Claude Sonnet 4.6

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This is an automatic backport of pull request #906 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 377b63c has failed:

On branch mergify/bp/humble/pr-906
Your branch is up to date with 'origin/humble'.

You are currently cherry-picking commit 377b63c.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   tf2_ros_py/tf2_ros/transform_listener.py

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[ahcorde]

Pulls: #915
Gist: https://gist.githubusercontent.com/ahcorde/6934930d088f4869c0395b1c63d92691/raw/96c708381fa91363f827610341550ff12c10cc5d/ros2.repos
BUILD args: --packages-above-and-dependencies tf2_ros_py
TEST args: --packages-above tf2_ros_py
ROS Distro: humble
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/18617

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