Fixed #28391 -- Fixed Cast() with CharField and max_length on MySQL.

Thanks Tim Graham for the review.

tests/db_functions/test_cast.py

@@ -1,7 +1,7 @@
 from django.db import models
 from django.db.models.expressions import Value
 from django.db.models.functions import Cast
-from django.test import TestCase
+from django.test import TestCase, ignore_warnings, skipUnlessDBFeature
 
 from .models import Author
 
@@ -19,6 +19,13 @@ class CastTests(TestCase):
         numbers = Author.objects.annotate(cast_string=Cast('age', models.CharField(max_length=255)),)
         self.assertEqual(numbers.get().cast_string, '1')
 
+    # Silence "Truncated incorrect CHAR(1) value: 'Bob'".
+    @ignore_warnings(module='django.db.backends.mysql.base')
+    @skipUnlessDBFeature('supports_cast_with_precision')
+    def test_cast_to_char_field_with_max_length(self):
+        names = Author.objects.annotate(cast_string=Cast('name', models.CharField(max_length=1)))
+        self.assertEqual(names.get().cast_string, 'B')
+
     def test_cast_to_integer(self):
         for field_class in (
             models.IntegerField,