ci: cancel in-flight runs when a PR is converted to draft

[goastler]

Same change as https://github.com/prosopo/captcha-private/pull/4113, applied here.

Adds converted_to_draft to the pull_request types of the nine PR-triggered workflows. Every one of them already has concurrency: cancel-in-progress: true, and that is what does the cancelling — a job-level if cannot stop a run that is already going. Adding the trigger type means a new run is created, claims the group, and evicts the in-flight one; the jobs then skip, so the new run costs nothing.

Seven of the nine need no new condition: they already gate on github.event.pull_request.draft == false, and on a converted_to_draft event the PR is draft, so they skip on their own. Two gate on something else and got an explicit github.event.action != 'converted_to_draft':

• changesets.yml (gates on the PR title)
• dependabot-changeset.yml (gates on the actor)

Out of scope: tag_release.yml (closed only) and release.yml.

Not verifiable from a draft PR — to prove it, convert a throwaway non-draft PR to draft while a run is in flight and watch the run get cancelled.