Disable refresh during update in Matrix8x8x2

In Matrix8x8x2.image(), store current auto_write state
in temp variable and set auto_write to False before
looping to update all pixels in the matrix. Once done
updating, restore auto_write state to previous setting.

Author: SAK917

adafruit_ht16k33/matrix.py

@@ -217,6 +217,8 @@ def image(self, img):
             )
         # Grab all the pixels from the image, faster than getpixel.
         pixels = img.convert("RGB").load()
+        auto_write = self.auto_write
+        self._auto_write = False
         # Iterate through the pixels
         for x in range(self.columns):  # yes this double loop is slow,
             for y in range(self.rows):  #  but these displays are small!
@@ -229,5 +231,6 @@ def image(self, img):
                 else:
                     # Unknown color, default to LED off.
                     self.pixel(x, y, self.LED_OFF)
+        self._auto_write = auto_write
         if self._auto_write:
             self.show()