Fixed #28431 -- Added a system check for BinaryField to prevent strings defaults.

Thanks Claude Paroz for the initial patch.

django/db/models/fields/__init__.py

@@ -2252,6 +2252,21 @@ class BinaryField(Field):
         if self.max_length is not None:
             self.validators.append(validators.MaxLengthValidator(self.max_length))
 
+    def check(self, **kwargs):
+        return [*super().check(**kwargs), *self._check_str_default_value()]
+
+    def _check_str_default_value(self):
+        if self.has_default() and isinstance(self.default, str):
+            return [
+                checks.Error(
+                    "BinaryField's default cannot be a string. Use bytes "
+                    "content instead.",
+                    obj=self,
+                    id='fields.E170',
+                )
+            ]
+        return []
+
     def deconstruct(self):
         name, path, args, kwargs = super().deconstruct()
         if self.editable: