Add default GORACE environment variable to race-detector enabled builds

[mark-rushakoff]

Per https://go.dev/doc/articles/race_detector, by default, a race-detector-enabled build will print data races to stderr and continue execution.

IMO, if someone is using the -race tagged builds, they are looking for fast feedback on the first data race encountered. Setting GORACE=halt_on_error=1 will cause the program to exit with code 66 on the first data race encountered, whereas the default value will continue execution to the end and probably exit 0.

I think the feedback would be clearer if defaulting to halt on error, and the user is always free to override it back to GORACE=halt_on_error=0 if they do want execution to continue past the first encountered data race.