Considering the variability in bot nickname postfixes, it might be impractical to assume that a digit will be appended for the IRC nick. From my observation a _ postfix appears to be more prevalent. I suggest the following approach:

// Verify if the nickname concludes with an asterisk and holds the correct prefix
if strings.HasSuffix(announcer, "*") && strings.HasPrefix(nick, announcer) {
    return true
}

// Confirm if the nickname starts with the announcer and comprises one additional character
if strings.HasPrefix(nick, announcer) && len(nick) == len(announcer)+1 {
    return true
}

Since IRC nicknames typically do not permit asterisks, this adjustment accommodates cases where an announcer ends with an asterisk in its definition. Additionally, I have omitted the requirement for the last character to be a digit, which was the original issue I anticipated.