ci: add support for merge_group in preview

[hollandjg]

as described here: https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/configuring-pull-request-merges/managing-a-merge-queue#triggering-merge-group-checks-with-github-actions

Todos once merged: add "require merge queue" in branch protection rules

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit 9030085):

https://ccv-brown-edu--pr192-ci-add-merge-queue-69kyu050.web.app

_{(expires Thu, 13 Jul 2023 18:33:35 GMT)}

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