fixing issue #15648
On failure, testing report would be like:

Sorry, in the issue report I meant make cov. https://github.com/bitcoin/bitcoin/blob/master/doc/developer-notes.md#compiling-for-test-coverage
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Reviewers, this pull request conflicts with the following ones:
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<!--cf906140f33d8803c4a75a2196329ecb-->Needs rebase
No activity for more than a month. Closing for now.