Update supported GitHub Enterprise Server versions #4579

Job	Run time
Config export (windows-latest, nightly-latest)	3m 29s
Config export (macos-latest, linked)	2m 14s
Config export (ubuntu-latest, linked)	1m 2s
Config export (ubuntu-latest, nightly-latest)	1m 17s
Config export (windows-latest, linked)	1m 41s
Config export (macos-latest, nightly-latest)	2m 2s
	11m 45s

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