Test

README: remove some references to older Go versions #125

Job	Run time
test-external-repos (terraform_chain)	5m 11s
test-external-repos (terraform_nochain)	5m 32s
test-gotip (ubuntu-latest)	54s
test (1.21.x, ubuntu-latest)	50s
test-gotip (macos-latest)	1m 50s
test (1.21.x, macos-latest)	1m 56s
test-gotip (windows-latest)	6m 8s
test (1.21.x, windows-latest)	3m 13s
test (1.20.x, ubuntu-latest)	45s
test (1.20.x, macos-latest)	1m 47s
test (1.20.x, windows-latest)	3m 2s
	31m 8s

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