JTC: Use std::atomic<bool> (backport #1720)

[mergify]

Apply changes from the guidelines added with ros-controls/realtime_tools#347

---

This is an automatic backport of pull request #1720 done by Mergify.

[mergify]

Cherry-pick of 0dcdd04 has failed:

On branch mergify/bp/humble/pr-1720
Your branch is up to date with 'origin/humble'.

You are currently cherry-picking commit 0dcdd04.
  (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:   joint_trajectory_controller/include/joint_trajectory_controller/joint_trajectory_controller.hpp
	both modified:   joint_trajectory_controller/src/joint_trajectory_controller.cpp

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.20%. Comparing base (1ebee52) to head (c82e8a4).
Report is 3 commits behind head on humble.

Additional details and impacted files

@@            Coverage Diff             @@
##           humble    #1722      +/-   ##
==========================================
- Coverage   67.21%   67.20%   -0.01%     
==========================================
  Files         122      122              
  Lines       14479    14476       -3     
  Branches     8945     8936       -9     
==========================================
- Hits         9732     9729       -3     
- Misses       1455     1461       +6     
+ Partials     3292     3286       -6     

Flag	Coverage Δ
unittests	67.20% <100.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...jectory_controller/joint_trajectory_controller.hpp	100.00% <ø> (ø)
...ory_controller/src/joint_trajectory_controller.cpp	81.86% <100.00%> (-0.07%)	⬇️

... and 1 file with indirect coverage changes

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