opam: Stop leaking temporary folders on machine during tests

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Migrated from D6637 (view on Phabricator)

Build is green

Patch application report for D6637 (id=24127)

Rebasing onto 6243f800...

Current branch diff-target is up to date.

Changes applied before test

commit 97553d8984eeff2e611537265431c813a31737b7
Author: Antoine R. Dumont (@ardumont) <ardumont@softwareheritage.org>
Date:   Wed Nov 10 16:58:35 2021 +0100

    opam: Stop leaking temporary folders on machine

See https://jenkins.softwareheritage.org/job/DLS/job/tests-on-diff/410/ for more details.

Merge request was accepted

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Merge request was merged

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