[Backport]controller_manager: Add space to string literal concatenation (#1245)

[roscan-tech]

Contributions via pull requests are much appreciated. Before sending us a pull request, please ensure that:

1. Limited scope. Your PR should do one thing or one set of things. Avoid adding “random fixes” to PRs. Put those on separate PRs.
2. Give your PR a descriptive title. Add a short summary, if required.
3. Make sure the pipeline is green.
4. Don’t be afraid to request reviews from maintainers.
5. New code = new tests. If you are adding new functionality, always make sure to add some tests exercising the code and serving as live documentation of your original intention.

To send us a pull request, please:

• Fork the repository.
• Modify the source; please focus on the specific change you are contributing. If you also reformat all the code, it will be hard for us to focus on your change.
• Ensure local tests pass. (colcon test and pre-commit run (requires you to install pre-commit by pip3 install pre-commit)
• Commit to your fork using clear commit messages.
• Send a pull request, answering any default questions in the pull request interface.
• Pay attention to any automated CI failures reported in the pull request, and stay involved in the conversation.

[mergify]

@roscan-tech, all pull requests must be targeted towards the master development branch.
Once merged into master, it is possible to backport to humble, but it must be in master
to have these changes reflected into new distributions.

[christophfroehlich]

Normally we use mergify to backport stuff. just ping someone of the maintainers in the original PR the next time :)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 62.29%. Comparing base (19c52a6) to head (41cd38f).
Report is 7 commits behind head on humble.

Additional details and impacted files

@@            Coverage Diff             @@
##           humble    #1747      +/-   ##
==========================================
- Coverage   62.30%   62.29%   -0.01%     
==========================================
  Files         105      105              
  Lines       11314    11315       +1     
  Branches     7925     7926       +1     
==========================================
  Hits         7049     7049              
- Misses        806      807       +1     
  Partials     3459     3459              

Flag	Coverage Δ
unittests	62.29% <ø> (-0.01%)	⬇️

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

Files with missing lines	Coverage Δ
controller_manager/src/controller_manager.cpp	66.78% <ø> (ø)