tests: use more portable variable initialization for 1.8 branch

[nokute78]

This PR is for v1.8 branch.
Original patch is #4196 and I cherry-picked.

Fixes #4255

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Testing
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[nokute78]

Merge this PR since I already reviewed #4196 and this is cherry-picked pull request.

[edsiper]

Please make sure the commits has the proper "prefix". For PRs where the title is OK but the commit different, by choosing the Squash option instead of rebase allows to override the commit message.

[nokute78]

@edsiper Sorry I forgot to point the prefix at #4196 . I will take care it.

For PRs where the title is OK but the commit different

Hmm, I think it should be checked by CI, but it checks PR title only...