Nevera can also be a variant for nevjera in the ekavian* dialect, eg. serbian language would use it (https://en.wiktionary.org/wiki/nevera#Serbo-Croatian). Although the stress is different (/něʋera/ vs /něʋeːra/).

(*) dialects on wikipedia:

https://en.wikipedia.org/wiki/Dialects_of_Serbo-Croatian#Div...

One of the provided examples has variations of the word "vjera" meaning faith in each dialect, ne-vjera is basically non-faith.

> faith věra vera vira vjera

Wiktionary is often the best dictionary for this kind of query: https://en.wiktionary.org/wiki/nevera