Your branches key looks like it is excessively indented, by one space. Could that be it?
If not, can you give some information about the ngh command? I wonder if you need to explain your workflow, too - I use GH Pages, and I do all the committing manually, and I can’t think of why my CI would modify the repo. I don’t use that binary though.
I just checked the config reference, and the jobs key needs to have zero indentation. Then, each of your build, branches, ignore should have exactly two indentation spaces more than the last one.