wiring: the devkit's CI fails on a dispatch it cannot read or a devkit listener with no sender #163

v0.15.0 shipped notify-devkit.yml with its type in a JSON literal, which wiring.py cannot read, and a
bump-merge.yml that listens for bump-ready. The devkit's CI was green; the first place that saw the orphan was
the umbrella's v0.15.0 bump PR (marola-dev/marola#862, wiring --check), after the release (#161). Two gaps:
wiring.py skips a /dispatches call whose type it cannot read, with no message, and nothing in the devkit's CI
runs the wiring rules on the devkit's own workflows.

Acceptance criteria

• wiring.py reports a step whose run calls /dispatches and yields no type it can read, as
  <repo> `<file>`: a dispatch whose type wiring cannot read; --check fails on it.
• New wiring.py --lint-devkit [DIR] (default: this repo): reads the devkit's own .github/workflows, resolves a
  workflow's call of ./.github/workflows/<f> or marola-dev/marola-devkit/.github/workflows/<f>@<any ref> to
  the working-tree <f>, and fails
  on (1) an unreadable dispatch as above, and (2) a repository_dispatch type a devkit workflow listens for that no
  devkit workflow sends.
• devkit-ci.yml runs it on every PR (in the python job's self-test commands or its own step), so a PR like notify-devkit: a consumer's green bump PR wakes bump-merge #158
  goes red before a release.
• wiring.py --self-test covers both failures: a JSON-literal body with no EVENT* env, and a listener with no sender.

Named test

• On a branch at v0.15.0 (8da577b), wiring.py --lint-devkit fails with both messages for bump-ready; on main
  after wiring sees no sender for bump-ready, so the umbrella's v0.15.0 bump is red #161 it passes.
• wiring.py --self-test and devkit-quality rc=0.