docs: fix grammatical error in upgrading to v15 guide (#81038)
Title is pretty self descriptive.
<img width="667" alt="image"
src="https://github.com/user-attachments/assets/211f9eee-5d39-494e-abb9-9cad996b75be"
/>
Removes the word "you" for better grammatical clarity.
Co-authored-by: Joseph <joseph.chamochumbi@vercel.com>
