rclc_executor: improve enum type names (backport #379)

This is an automatic backport of pull request #379 done by Mergify. Cherry-pick of 14c2c412522f34114c335d0d760a3f54c0cac656 has failed:

On branch mergify/bp/humble/pr-379
Your branch is up to date with 'origin/humble'.

You are currently cherry-picking commit 14c2c41.
  (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:   rclc/src/rclc/executor.c
    modified:   rclc/test/rclc/test_executor.cpp

Unmerged paths:
  (use "git add <file>..." to mark resolution)
    both modified:   rclc/include/rclc/executor.h

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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ros2 / rclc

rclc_executor: improve enum type names (backport #379) #383