This is, perhaps, a judgement call. I would correct them. There may be "reasons" why the original wasn't accurate, even if it is just not knowing how to produce the letters of an expanded alphabet on your keyboard. I suspect, but don't know, that the diacritics might actually change the meaning in a few cases. But in this case it is proper to "honor" the person named even if it is a bit out of sync with the one doing the citing.
But others might disagree, believing that, when quoting, it is necessary to be precise.
A solution, of course, is to put the corrected name (or other word) in parentheses, following a quote. Or, some would write ... Angel [sic]... to indicate that the original is being preserved even though incorrect.
I'll also note that search engines seem to be sensitive to this issue and find the item correctly. For example searching Google or Duck Duck Go for "Gabriel Garcia Marquez" behaves correctly even when the name is in actual quotes. It also finds items that don't correctly accent the name. Likewise a search that has the proper accents finds items that don't.