Corrects 200+ instances of "it's" where it should've been "its" instead (#85169)

## About The Pull Request

it's - conjunction of "it" and "is"
its - possessive form of "it"

grammar is hard, and there were a lot of places where "it's" was used
where it shouldn't have been. i went and painstakingly searched the
entire repository for these instances, spending a few hours on it. i
completely ignored the changelog archive, and i may have missed some
outliers. most player-facing ones should be corrected, though
## Why It's Good For The Game
proper grammar is good

## Changelog
🆑
spellcheck: Numerous instances of "it's" have been properly replaced
with "its"
/🆑

code/game/objects/items/granters/magic/knock.dm

@@ -9,7 +9,7 @@
 		"Slow down, book. I still haven't finished this page...",
 		"The book won't stop moving!",
 		"I think this is hurting the spine of the book...",
-		"I can't get to the next page, it's stuck t- I'm good, it just turned to the next page on it's own.",
+		"I can't get to the next page, it's stuck t- I'm good, it just turned to the next page on its own.",
 		"Yeah, staff of doors does the same thing. Go figure...",
 	)