upgrade: rename actions to upgrade_actions
The `actions` were a list of optimizations and format upgrades which will be
upgraded. This does not include things which will be downgraded.
Let's rename the variable for clarity. It now makes obvious that we don't have
any concrete information on what things are downgraded.
Differential Revision: https://phab.mercurial-scm.org/D9616
edition = "2018"
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wrap_comments = true
error_on_line_overflow = true