We currently generate invalid workflow commands when we create
annotations with a `title` but no `file`. Let's fix that.
While we're here, let's improve handling of `title`s with `:`s. We
cannot use `title`s with `::` since GitHub Actions uses this as a
separator for different fields between a workflow command.
Let's also make sure `metadata` never ends in a `:` to avoid confusing
the GitHub Actions command parser about where the `::` separator is
meant to be.
54383d1c5f