Update supported GitHub Enterprise Server versions #6421

Job	Run time
Ruby analysis (macos-latest, linked)	1m 7s
Ruby analysis (ubuntu-latest, default)	44s
Ruby analysis (macos-latest, default)	50s
Ruby analysis (ubuntu-latest, linked)	48s
Ruby analysis (macos-latest, nightly-latest)	53s
Ruby analysis (ubuntu-latest, nightly-latest)	46s
	5m 8s

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