Fix the restoring of os.environ to maintain type. (backport #656)

This is an automatic backport of pull request #656 done by Mergify. Cherry-pick of a36e9b945076ba9c0fbc1e9807600ed630a16ede has failed:

On branch mergify/bp/galactic/pr-656
Your branch is up to date with 'origin/galactic'.

You are currently cherry-picking commit a36e9b9.
  (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)

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
    both modified:   launch/launch/launch_context.py
    deleted by us:   launch/test/launch/actions/test_push_and_pop_environment.py

no changes added to commit (use "git add" and/or "git commit -a")

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

Mergify commands and options

More conditions and actions can be found in the [documentation](https://docs.mergify.com/). You can also trigger Mergify actions by commenting on this pull request: - `@Mergifyio refresh` will re-evaluate the rules - `@Mergifyio rebase` will rebase this PR on its base branch - `@Mergifyio update` will merge the base branch into this PR - `@Mergifyio backport ` will backport this PR on `` branch Additionally, on Mergify [dashboard](https://dashboard.mergify.com/) you can: - look at your merge queues - generate the Mergify configuration with the config editor. Finally, you can contact us on https://mergify.com

ros2 / launch

Fix the restoring of os.environ to maintain type. (backport #656) #661