address context shutdown racy condition. (backport #3219)

[mergify]

Description

retarget #3217 to lyrical

Fixes # (issue)

Is this user-facing behavior change?

Did you use Generative AI?

Additional Information

---

This is an automatic backport of pull request #3219 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of b723878 has failed:

On branch mergify/bp/jazzy/pr-3219
Your branch is up to date with 'origin/jazzy'.

You are currently cherry-picking commit b723878.
  (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)

Changes to be committed:
	modified:   rclcpp/src/rclcpp/signal_handler.cpp
	modified:   rclcpp/test/rclcpp/test_context.cpp

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   rclcpp/src/rclcpp/context.cpp

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

[mergify]

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[fujitatomoya]

Pulls: #3225
Gist: https://gist.githubusercontent.com/fujitatomoya/4fb035ab945c5605f7c910030b8529d2/raw/ef4de8a5e03fe47661e060880eed57953053efd2/ros2.repos
BUILD args: --packages-above-and-dependencies rclcpp
TEST args: --packages-above rclcpp
ROS Distro: jazzy
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/20072

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