Dependabot: Remove deprecated `reviewers` config #4204

Job	Run time
Diagnostic export (ubuntu-latest, nightly-latest)	1m 2s
Diagnostic export (ubuntu-latest, linked)	1m 4s
Diagnostic export (windows-latest, linked)	2m 35s
Diagnostic export (windows-latest, nightly-latest)	3m 49s
Diagnostic export (macos-latest, nightly-latest)	1m 12s
Diagnostic export (macos-latest, linked)	1m 9s
	10m 51s

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