Yea has been used online as a synonym for yeah for going on 2 decades at this point. 

Appreciate they’re both spelt the same, but context clues should help you differentiate. For example, this is a comment on a social media platform, not a spokesperson in a decision making chamber, such as a house of representatives or boardroom; therefore we can safely assume it’s a person agreeing with a statement and not someone calling for a vote.