Thanks for your responses.
It does look like this is a bug in the editor, and as you rightly stated @DaveTheCoder it is because the integer division occurs twice on the same line
So:
@warning_ignore("integer_division")
result = n1 / n2
Happily ignores the warning about n1 and n2 being integers.
I did try multiple ignore statements, and @warning_ignore("integer_division", "integer_division") but they still persisted. I also do not want to disable the warning project wide as this is what I class as a gdscript quirk (it doesn't make obvious sense) so want to be warned if I do it elsewhere incase it is not expected.
So I have opted for the casting of them to float (thanks @xyz) whilst I disagree it is clearer and my OCD says it is sub optimal, for the sake of this problem it works
Cheers