Lower the max length for a test field so that it works on MySQL.

tests/get_or_create/models.py

@@ -31,7 +31,7 @@ class Profile(models.Model):
 
 
 class Tag(models.Model):
-    text = models.CharField(max_length=256, unique=True)
+    text = models.CharField(max_length=255, unique=True)
 
 
 class Thing(models.Model):