Send terminal control code to `STDOUT` instead

`STDERR` might be redirected, and this code signals to the terminal to
show the cursor again. Otherwise, the cursor will be invisible.

core/testing/runner.odin

@@ -667,7 +667,7 @@ runner :: proc(internal_tests: []Internal_Test) -> bool {
 		}
 	}
 
-	fmt.wprint(batch_writer, ansi.CSI + ansi.DECTCEM_SHOW)
+	fmt.wprint(stdout, ansi.CSI + ansi.DECTCEM_SHOW)
 
 	fmt.wprintln(stderr, bytes.buffer_to_string(&batch_buffer))