I thought to myself, "I wonder if it's possible to use a sneaky hacky
`content_for` trick to be able to run this code in the template." And
indeed it is!
It's tricky cuz like, I want to render this template, and I want to
provide _multiple_ slots of content to it. So, in this variant, we keep
the block as being primarily for the actions, but also optionally
accept `content_for :subtitle` inside that block, too.
Executing that correctly is a bit tricky! The subtitle comes *before*
the actions. So, we `yield` the actions block immediately, save it to a
variable, and *then* get the subtitle block.