chore(github): revert mergify config

[plumpy]

Reverts #673

I'm fairly certain this turns every reviewer into an approver. (Reviewers have the triage permission, which allows them to add labels.)

Merging this without a review, since you did too 😉

[spinnakerbot]

The following commits need their title changed:

• d430a98: Revert "chore(github): test out mergify config (chore(github): test out mergify config #673)"

Please format your commit title into the form:

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[marchello2000]

@plumpy thanks for reverting this and sorry about this - my understanding from @robzienert was that only approvers can add labels. I will follow up with him on that