Update supported GitHub Enterprise Server versions #751

Job	Run time
Upload debug artifacts after failure in analyze (default)	3m 9s
Upload debug artifacts after failure in analyze (stable-v2.20.3)	1m 47s
Upload debug artifacts after failure in analyze (nightly-latest)	2m 58s
Upload debug artifacts after failure in analyze (linked)	3m 3s
Download and check debug artifacts after failure in analyze	10s
	11m 7s

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