Fixed typos (backport #692)

[mergify]

This is an automatic backport of pull request #692 done by Mergify.
Cherry-pick of 2a84352 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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[adityapande-1995]

@osrf-jenkins retest this please