Dependabot: Remove deprecated `reviewers` config #3782

Job	Run time
Resolve environment (macos-latest, default)	1m 50s
Resolve environment (ubuntu-latest, default)	32s
Resolve environment (windows-latest, default)	2m 6s
Resolve environment (ubuntu-latest, nightly-latest)	34s
Resolve environment (windows-latest, linked)	3m 58s
Resolve environment (macos-latest, nightly-latest)	2m 24s
Resolve environment (macos-latest, linked)	2m 19s
Resolve environment (ubuntu-latest, linked)	32s
Resolve environment (windows-latest, nightly-latest)	4m 15s
	18m 30s

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