There is a feeling that poles do not really like or welcome russians
IME Polish people officially don't like Russians in general but are ready and willing to make exceptions for Russians they know (especially if they can speak Polish and it will be super simple to learn once you're here). Many Poles like the aesthetics of Russian culture, it's the history and (current) politics they don't like.
In a pinch, say you're Ukrainian since most can't tell the difference in accents (is there one?) and relations between Poland and Ukraine are about as good as they've ever been. Okay that's too far, but still there shouldn't be any problem in Warsaw.