It's actually standard colloquial pronunciation in virtually all dialects of English.
No matter how fervently some native English speakers may protest it, that is the case. The only exceptions I can think of is the English spoken by the Queen of England (possibly) and that used by the Italian Mob characters in The Simpsons, whose aversion to elision is part of their whole shtick.
For an English learner to use these spellings in a written English exam such as IELTS would be a solecism, I think we all agree on that.
Go
Tomorrow I am _ to the cinema.
Answer:
Tomorrow I am gonna go to the cinema, innit, lol :)
A student should not expect top marks for that.
On an internet forum? Acceptable. Write how you speak, if you fancy.
What about “proper” writing?
"Literature got me into this and literature is gonna have to get me out" - Philip Roth.