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.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.87%. Comparing base (7df20f6) to head (643604c).
Report is 5 commits behind head on jazzy.

Additional details and impacted files

@@           Coverage Diff           @@
##            jazzy    #1723   +/-   ##
=======================================
  Coverage   84.86%   84.87%           
=======================================
  Files         127      127           
  Lines       12147    12144    -3     
  Branches     1036     1035    -1     
=======================================
- Hits        10309    10307    -2     
  Misses       1499     1499           
+ Partials      339      338    -1     

Flag	Coverage Δ
unittests	84.87% <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	85.61% <100.00%> (-0.04%)	⬇️

... and 1 file with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.