[JTC] Fix typos, implicit cast, const member functions (backport #748)

[mergify]

This is an automatic backport of pull request #748 done by Mergify.
Cherry-pick of 6b73cf5 has failed:

On branch mergify/bp/humble/pr-748
Your branch is up to date with 'origin/humble'.

You are currently cherry-picking commit 6b73cf5.
  (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:   joint_trajectory_controller/src/joint_trajectory_controller_parameters.yaml
	modified:   joint_trajectory_controller/test/test_trajectory_controller.cpp

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
	both modified:   joint_trajectory_controller/test/test_trajectory_controller_utils.hpp

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[christophfroehlich]

included in #801