Defined by default collation is not respected when a charset is supplied

Issue description

For backwards compatibility, default collation set is defined as collation-server = utf8mb3_general_ci in my.cnf file.

However, this value is being ignored as default one, and utf8mb3_uca1400_ai_ci is being set to all new databases and tables.

This causes issues, like "Illegal mix of collations (utf8mb3_general_ci,IMPLICIT) and (utf8mb3_uca1400_ai_ci,IMPLICIT) for operation '='" when attempt to apply migrations or do some altering on previously created tables.

The issue happens only when table has a default charset supplied, ie CREATE TABLE `x` (...) DEFAULT CHARSET=utf8mb3;.
In case CHARSET is not provided - it respects defined collation.

How to reproduce

1. Add collation-server = utf8mb3_general_ci to my.cnf and restart server. Ensure collate is set:

   MariaDB [(none)]> SHOW VARIABLES LIKE 'collation_server';

   +------------------+--------------------+

   | Variable_name | Value |

   +------------------+--------------------+

   | collation_server | utf8mb3_general_ci |

   +------------------+--------------------+

   1 row in set (0.001 sec)

   MariaDB [(none)]>

2. Create new test database and ensure it's collation:

   MariaDB [(none)]> create database test_db;

   Query OK, 1 row affected (0.014 sec)

   MariaDB [(none)]> SELECT default_character_set_name, default_collation_name

   -> FROM information_schema.schemata

   -> WHERE schema_name = 'test_db';

   +----------------------------+------------------------+

   | default_character_set_name | default_collation_name |

   +----------------------------+------------------------+

   | utf8mb3 | utf8mb3_general_ci |

   +----------------------------+------------------------+

   1 row in set (0.001 sec)

3. Create test table and check it's collation

   MariaDB [(none)]> use test_db;

   Database changed

   MariaDB [test_db]> CREATE TABLE `x509keypair` (

   -> `id` int(11) NOT NULL AUTO_INCREMENT,

   -> `created_at` datetime DEFAULT NULL,

   -> `updated_at` datetime DEFAULT NULL,

   -> `uuid` varchar(36) DEFAULT NULL,

   -> `certificate` text DEFAULT NULL,

   -> `private_key` text DEFAULT NULL,

   -> `project_id` varchar(255) DEFAULT NULL,

   -> `user_id` varchar(255) DEFAULT NULL,

   -> `intermediates` text DEFAULT NULL,

   -> `private_key_passphrase` text DEFAULT NULL,

   -> PRIMARY KEY (`id`),

   -> UNIQUE KEY `uniq_x509keypair0uuid` (`uuid`)

   -> ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb3;

   Query OK, 0 rows affected (0.025 sec)

   MariaDB [test_db]>

   MariaDB [test_db]> SELECT table_name, column_name, collation_name FROM information_schema.columns WHERE table_schema = 'test_db';

   +-------------+------------------------+-----------------------+

   | table_name | column_name | collation_name |

   +-------------+------------------------+-----------------------+

   | x509keypair | id | NULL |

   | x509keypair | created_at | NULL |

   | x509keypair | updated_at | NULL |

   | x509keypair | uuid | utf8mb3_uca1400_ai_ci |

   | x509keypair | certificate | utf8mb3_uca1400_ai_ci |

   | x509keypair | private_key | utf8mb3_uca1400_ai_ci |

   | x509keypair | project_id | utf8mb3_uca1400_ai_ci |

   | x509keypair | user_id | utf8mb3_uca1400_ai_ci |

   | x509keypair | intermediates | utf8mb3_uca1400_ai_ci |

   | x509keypair | private_key_passphrase | utf8mb3_uca1400_ai_ci |

   +-------------+------------------------+-----------------------+

   10 rows in set (0.008 sec)

   MariaDB [test_db]>