Test go generate error handling in mechanical checks

-- go.mod --
module sketch.dev

go 1.23

-- .commit --
Initial commit

-- main.go --
package main

//go:generate false

func main() {
	println("Hello, world!")
}

-- .commit --
Commit with failing go generate directive

-- .run_test --
# Errors

$ go generate sketch.dev
main.go:3: running "false": exit status 1


Please fix before proceeding.