Update supported GitHub Enterprise Server versions #4456

Job	Run time
Diagnostic export (windows-latest, linked)	2m 31s
Diagnostic export (ubuntu-latest, nightly-latest)	1m 27s
Diagnostic export (ubuntu-latest, linked)	1m 12s
Diagnostic export (windows-latest, nightly-latest)	2m 53s
Diagnostic export (macos-latest, linked)	2m 23s
Diagnostic export (macos-latest, nightly-latest)	1m 59s
	12m 25s

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