Briefly, in #5622, we required that certain margin elements in the theme are of the class 'margin'.
However, reverse dependency checks shows that many people use e.g. theme(plot.margin = unit(c(4, 4, 4, 4), "mm").
This isn't necessarily wrong, so this PR allows margin elements to accept units too.
This PR is an amendement to #5622.
Briefly, in #5622, we required that certain margin elements in the theme are of the class 'margin'. However, reverse dependency checks shows that many people use e.g.
theme(plot.margin = unit(c(4, 4, 4, 4), "mm"). This isn't necessarily wrong, so this PR allows margin elements to accept units too.