Issue test which I think is a bug

[123sarahj123]

We're seeing an issue where the buildkite agent fails to parse the JSON-formatted pipeline file we're passing to buildkite-agent pipeline upload:

Pipeline parsing of "tmpjdd2BG" failed (Failed to parse tmpjdd2BG: line 531: found invalid Unicode character escape code)

I was able to reproduce the issue on the Go Playground using the same YAML library that the agent uses. The Go standard library JSON parser handles the input without an issue.

I found a related issue on the upstream go-yaml project.