Fixed #35000 -- Skipped declaring empty string defaults on BLOB/TEXT field on MySQL.

Empty string defaults are redundant on MySQL and prevent use of
ALGORITHM=INSTANT.

django/db/backends/mysql/schema.py

@@ -69,12 +69,22 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             and db_type.lower() in self.connection._limited_data_types
         )
 
+    def _is_text_or_blob(self, field):
+        db_type = field.db_type(self.connection)
+        return db_type and db_type.lower().endswith(("blob", "text"))
+
     def skip_default(self, field):
+        default_is_empty = self.effective_default(field) in ("", b"")
+        if default_is_empty and self._is_text_or_blob(field):
+            return True
         if not self._supports_limited_data_type_defaults:
             return self._is_limited_data_type(field)
         return False
 
     def skip_default_on_alter(self, field):
+        default_is_empty = self.effective_default(field) in ("", b"")
+        if default_is_empty and self._is_text_or_blob(field):
+            return True
         if self._is_limited_data_type(field) and not self.connection.mysql_is_mariadb:
             # MySQL doesn't support defaults for BLOB and TEXT in the
             # ALTER COLUMN statement.