Dependabot: Remove deprecated `reviewers` config #6913

Job	Run time
Split workflow (ubuntu-latest, nightly-latest)	1m 8s
Split workflow (ubuntu-latest, linked)	1m 8s
Split workflow (macos-latest, default)	1m 18s
Split workflow (macos-latest, nightly-latest)	1m 43s
Split workflow (ubuntu-latest, default)	1m 8s
Split workflow (macos-latest, linked)	1m 33s
	7m 58s

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