Create auto-merge-dev-deps.yml

[sndrs]

What is the purpose of this change?

have dev dep bumps auto merge

What does this change?

adds a new action based on https://github.com/dependabot/fetch-metadata

dont know if we'd need to auto-approve too https://github.com/dependabot/fetch-metadata#auto-approving

[changeset-bot]

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Latest commit: 495ec91

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[SiAdcock]

Let's see this in action 👍

[sndrs]

i'm not sure this will work with our branch restricitions, but do like the look of this: https://github.com/hrvey/combine-prs-workflow