ERP5-py3: fix repozo backup generation

See merge request !1665
7 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed Cloudooo.UnitTest-Master

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passed ERP5.StandaloneDeploymentScriptTest-Debian.Buster

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passed SlapOS.Eggs.UnitTest-Master.Python2

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passed SlapOS.Eggs.UnitTest-Master.Python3

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passed SlapOS.Eggs.UnitTest-Master.Python3Next

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passed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster

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passed ERP5.StandaloneDeploymentScriptTest-Debian.Buster

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