Fixed typos (backport #692)

This is an automatic backport of pull request #692 done by Mergify. Cherry-pick of 2a8435222482e2dc20b16a9e039923f1885f2f4f has failed:

On branch mergify/bp/humble/pr-692
Your branch is up to date with 'origin/humble'.

You are currently cherry-picking commit 2a84352.
  (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:   launch/launch/actions/execute_process.py
    modified:   launch/launch/descriptions/executable.py
    modified:   launch/launch/event_handlers/on_action_event_base.py
    modified:   launch/launch/frontend/expose.py
    modified:   launch/launch/frontend/parser.py
    modified:   launch/launch/launch_description.py
    modified:   launch/launch/substitutions/environment_variable.py
    modified:   launch/launch/utilities/__init__.py
    modified:   launch/test/launch/frontend/test_expose_decorators.py
    modified:   launch/test/launch/test_launch_description.py
    modified:   launch/test/launch/utilities/test_class_tools.py
    modified:   launch/test/launch/utilities/test_ensure_argument_type.py
    modified:   launch_pytest/README.md
    modified:   launch_testing/README.md
    modified:   launch_testing/launch_testing/asserts/assert_sequential_output.py
    modified:   launch_testing/test/launch_testing/examples/context_launch_test.py
    modified:   launch_testing/test/launch_testing/test_sequential_output_checker.py
    modified:   launch_xml/launch_xml/entity.py

Unmerged paths:
  (use "git add <file>..." to mark resolution)
    both modified:   launch/launch/substitutions/python_expression.py

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 / launch

Fixed typos (backport #692) #693