https://twitter.com/tyomateee2/status/1440691228115230731
イッヌ「ご主人!がんばって!」
In the above dog-related tweet, 犬 seems to be spelled as 'イッヌ' rather than 'イヌ'. Is the presence of 'ッ' a typo or is it a stylistic choice? If it's not a typo, are there circumstances where you should use write ッヌ instead of ンヌ in a word?