always run changelog.d

We've made this a required job to ensure that changelogs are
always valid. But this means we can't use "paths", or PRs that
don't have changelogs will stall because the changelogs job
doesn't get run so it's never considered "succeeded".

This job is cheap, so run it unconditionally. We already know
things are currently valid, so this shouldn't produce any
surprises.