z80 "The function 'shell_open()' returns a value, but this value is never used."
That warning can be suppressed by preceding the line with:
#warning-ignore:RETURN_VALUE_DISCARDED
You can save some time and have the editor insert that by clicking on the little yellow triangle at the bottom right of the script window and then clicking on [Ignore]
.
You can also disable warnings globally, but I prefer not to do that, since sometimes the warning indicates an actual mistake:
Project >> Project Settings... >> General >> Debug >> GDScript