build: BIN value must use single-path GOPATH value

[shoenig]

I broke the build due to #12077 not using our workaround for GOPATH

2nd time I've been burned by https://discuss.circleci.com/t/gopath-is-set-to-multiple-directories/7174

Circle: 2 Seth: 0

BIN is /home/circleci/.go_workspace:/usr/local/go_workspace/bin

=== Failed
=== FAIL: command TestIntegration_Command_RoundTripJob (0.13s)
...
    integration_test.go:57: 
        	Error Trace:	integration_test.go:57
        	Error:      	Expected nil, but got: &exec.Error{Name:"nomad", Err:(*errors.errorString)(0xc000129190)}
        	Test:       	TestIntegration_Command_RoundTripJob
    integration_test.go:66: error running example.nomad: exec: "nomad": executable file not found in $PATH

[lgfa29]

Thanks! I saw that error in a branch and I thought I had broken it 😅

[github-actions]

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