Fix catalog getitem to work with numpy int index #906
@mirca - Thanks!
I just now remembered that I saw
They define it slightly differently, and I'd prefer we do it the same way (just because I don't know if there's any difference / details we're not aware of).
My suggestion would be that here in Gammapy, we don't call it directly, because it's private in Astropy and might change. Instead, let's define our own utility function
Then import it from this catalog file and call it.
Usually I put changelog entries after I merge something in Gammapy, but if you put it yourself, that is fine as well of course.