Add tests for getCredentials with multiple goproxy_servers and maven_… #3265

Job	Run time
Upload debug artifacts (linked)	6m 7s
Upload debug artifacts (default)	6m 2s
Upload debug artifacts (stable-v2.20.3)	5m 39s
Upload debug artifacts (nightly-latest)	5m 41s
Download and check debug artifacts	6s
	23m 35s

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