draw_text8x8: Fix off-by-one

[fearnoeval]

Steps to reproduce

display.draw_text8x8(15 * 8, 0, "A")
display.draw_text8x8(0, 7 * 8, "A")

# x-coordinate: 128 above maximum of 127.
# y-coordinate: 64 above maximum of 63.

Rationale

• Coordinates (120, 0) or (0, 56) are within range for 8x8 text

Other

• Additionally, the draw_text8x8 doesn't check how long the string is, so the bounds check can be bypassed that way, though I don't consider it much of an issue since the underlying FrameBuffer.text implementation appears to ignore anything out-of-bounds