refactor(network): call app.Close() on network cleanup (backport #18249)

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This is an automatic backport of pull request #18249 done by Mergify.
Cherry-pick of 139a29e has failed:

On branch mergify/bp/release/v0.47.x/pr-18249
Your branch is up to date with 'origin/release/v0.47.x'.

You are currently cherry-picking commit 139a29e7e.
  (fix conflicts and run "git cherry-pick --continue")
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Unmerged paths:
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	both modified:   testutil/network/network.go
	both modified:   testutil/network/util.go

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

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