Gonna hope this doesn't use the merge ref and is good enough

* Dependabot changelogs: trigger CI explicitly

* Changelog

* Use merge ref, not head ref

ref ref ref ref ref

* explanatory note

Fixes a typo in #14021, and allows the workflow to trigger on `reopen`
for easier debugging.

* yet another attempt to make dependabot changelogs work

* Changelog

* Try again to automate dependabot changelogs

* Changelog

* Change dependabot CL suffix

* Changelog