fix: GCECredentials lazily fetches from the metadata server to ensure a universe domain is known #558

Job	Run time
CI (ubuntu-20.04, 3.0, test , spec)	1m 51s
CI (ubuntu-20.04, 3.1, test , spec)	1m 57s
CI (ubuntu-22.04, 3.2, test , spec)	2m 22s
CI (ubuntu-latest, 3.3, test , spec)	2m 24s
CI (macos-latest, 3.3, test , spec)	1m 16s
CI (windows-latest, 3.3, test , spec)	3m 3s
CI (ubuntu-latest, 3.3, rubocop , integration , build , yardoc , linkinator)	31s
	13m 24s

Provide feedback