Corrected border position for P mode in ImageOps.expand()

[radarhere]

Resolves #5375

After #5552, running the code from that issue, there is a unintended line on the right and bottom of the image.

Pillow/src/PIL/ImageOps.py

Line 402 in 28330c2

draw.rectangle((0, 0, width, height), outline=color, width=border)

I would have just forgotten that

https://pillow.readthedocs.io/en/stable/reference/ImageDraw.html#PIL.ImageDraw.ImageDraw.rectangle

The second point is just outside the drawn rectangle.

Fixing that, I get