[BUG] `refresh_db` is deprecated for `pkgrepo.managed`

[myii]

Your setup

Formula commit hash / release tag

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Bug details

Describe the bug

Same issue as saltstack-formulas/apt-formula#61.

• https://travis-ci.org/github/myii/letsencrypt-formula/jobs/681358913#L1673-L1686

Steps to reproduce the bug

Expected behaviour

Attempts to fix the bug

Additional context