Warn on older versions of func #20

Job	Run time
test-invalid-version	3s
test-default-latest (ubuntu-latest)	7s
test-default-latest (macos-latest)	10s
test-custom-version	5s
test-default-latest (windows-latest)	18s
test-custom-name	6s
test-custom-binary-source	5s
test-custom-destination	5s
	59s

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