Long story short; goto will result is a runtime jump, variable definition/declaration will result in storage allocation, compile time.
The compiler will see and decide on how much storage to allocate for an int, it will also make so that this allocated storage will be set to 3 when “hitting” i = 3;.
That memory location will be there even if there is a goto at the start of your function, before the declaration/definition, just as in your example.
Very silly simile
If I place a log on the ground and my friend runs (with his eyes closed) and jumps over it, the log will still be there – even if he hasn’t seen or felt it.
It’s realistic to say that he could turn around (at a later time) and set it on fire, if he wanted to. His jump doesn’t make the log magically disappear.