ci: run CI and Quality workflows on merge_group

[bburda]

Pull Request

Summary

main is getting a merge queue. A queue builds a temporary gh-readonly-queue/* branch and fires the merge_group event, and a workflow that triggers only on pull_request and push never runs there, so its checks never report and every queue entry times out. ci.yml and quality.yml now also run on merge_group.

Nothing else changes. The jobs gated on github.event_name == 'push' (coverage, notify-demos) stay skipped on the queue branch as they are on pull requests, and the clang-tidy job falls back to its full-tree scan there because there is no pull request diff to narrow it to.

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Issue

No issue. Two on: blocks, needed before the queue can be enabled.

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Type

• Bug fix
• New feature or tests
• Breaking change
• Documentation only

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Testing

• Both workflow files parse; the diff is the on: block in each and nothing else.
• The event syntax is the documented form from "Events that trigger workflows" (merge_group: types: [checks_requested]).
• The first queued merge after this lands is the test: every required check must report on the merge_group run.

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Checklist

• Breaking changes are clearly described (and announced in docs / changelog if needed)
• Tests were added or updated if needed
• Docs were updated if behavior or public API changed