Fix the deadlock in the destructor of RealtimePublisher (backport #320)

[mergify]

Fixes: ros-controls/ros2_controllers#1574
Fixes: ros-controls/ros2_controllers#1669

Apart from this, I've seen a possible vulnerability with the current API, I'll open a different PR to handle this one.

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This is an automatic backport of pull request #320 done by Mergify.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 72.63%. Comparing base (68ab384) to head (f29f167).

Files with missing lines	Patch %	Lines
include/realtime_tools/realtime_publisher.hpp	60.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           humble     #324      +/-   ##
==========================================
- Coverage   72.79%   72.63%   -0.16%     
==========================================
  Files          10       10              
  Lines         577      581       +4     
  Branches      220      223       +3     
==========================================
+ Hits          420      422       +2     
  Misses        105      105              
- Partials       52       54       +2     

Flag	Coverage Δ
unittests	72.63% <60.00%> (-0.16%)	⬇️

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

Files with missing lines	Coverage Δ
include/realtime_tools/realtime_publisher.hpp	87.71% <60.00%> (-2.85%)	⬇️

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