Your edit suggestion had two reject votes and one approval vote, and I was one of the votes to reject the edit. Normally I would've approved the sort of small edit you made if it was made to a new post, however you made this small edit to a very old answer, and edits to old posts are generally discouraged if it doesn't make a substantial change.
In the help center, you can see how editing is intended to work on this page. The relevant parts for your edit:
Tiny, trivial edits are discouraged - try to make the post significantly better when you edit, correcting all problems that you observe.
Editing a post also bumps the question to the top of the homepage. Please be mindful of this and make your edits count, so that the new attention is brought to something substantial.
Fixing grammar on a couple words is a pretty minor fix: I don't think it's a 'tiny' or 'trivial' one, but it also doesn't really make the post 'significantly better' so it's kind of a borderline case. But that answer that you edited is nearly a decade old, and the second point from the help center suggests that editing old posts should be done if it will bring attention to 'something substantial'. Putting both of those together, I didn't think I should accept the edit.
In short, fixing a couple words on a new post is probably fine, making significant fixes to an old post is also probably fine, but just fixing a couple words on an old post isn't really worthwhile.