Flush stdout on print to ensure it appears in systemd's journal logs

This ensures release builds use the same behavior as debug builds here.
The benchmarks project does not spam print messages anyway, so performance
should be identical to before.

project.godot

@@ -13,6 +13,7 @@ config_version=5
 config/name="Godot Benchmarks"
 run/main_scene="res://main.tscn"
 config/features=PackedStringArray("4.3")
+run/flush_stdout_on_print=true
 config/icon="res://icon.png"
 
 [autoload]