Fix data race in bootstrap.go
Fix data race in bootstrap.go

In bootstrap.go, we were accessing a variable `ctx` in a goroutine, but further down in the function, the `ctx` variable was being wrapped with a different context and set to the new value, so the goroutine was pointing at a value that had been reset.

The simple solution is to access `ctx` after it's been wrapped

buildkite/agent,buildkite/agent,buildkite/agent