The Constitution gives no role in the appointment of electors to the governor. It is solely the responsibility of the Legislature - no governor veto allowed.
You are correct, however, this is just one of various election issues which would be taken to court.
Suppose that there is chaos in vote counting in PA. The Republican legislature awards the Electoral votes to Trump, based on him leading in the vote count. The Dem. governor vetoes it. Then Democrats file suit in federal court, to prevent the Republican legislature’s chosen electors from being selected to perform in the Electoral college. Then, it would be up to courts, possibly the US Supreme Court, to rule on the procedure for choosing electors to the electoral college.
You saw that little “non-veto” point as well, didn’t you?