Fix argument order in the Windows implementation of getEnvOs (backport #11855)

[mergify]

Motivation

See the build failure in msys2/MINGW-packages#22499

Context

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CC @puffnfresh

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This is an automatic backport of pull request #11855 done by Mergify.

[mergify]

Cherry-pick of 355f08a has failed:

On branch mergify/bp/2.24-maintenance/pr-11855
Your branch is up to date with 'origin/2.24-maintenance'.

You are currently cherry-picking commit 355f08a72.
  (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 <file>..." to mark resolution)
	both modified:   src/libutil/windows/environment-variables.cc

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/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[Ericson2314]

Manual backport already done.