Add support for MetaBox relationships #54

Job	Run time
test / Get base test matrix	1s
test / Prepare matrix for unit tests	3s
test / Prepare matrix for functional tests	6s
test / Unit test / PHP ${{ matrix.php }}	0s
test / Functional - WP latest on PHP 8.0 with MySQL 8.0	1m 10s
test / Functional - WP latest on PHP 8.0 with SQLite	1m 7s
test / Functional - WP latest on PHP 8.1 with MySQL 8.0	1m 11s
test / Functional - WP latest on PHP 8.1 with SQLite	52s
test / Functional - WP latest on PHP 8.2 with MySQL 8.0	1m 23s
test / Functional - WP latest on PHP 8.2 with SQLite	1m 8s
test / Functional - WP trunk on PHP 8.0 with MySQL 8.0	1m 13s
test / Functional - WP trunk on PHP 8.0 with MySQL 5.7	1m 26s
test / Functional - WP trunk on PHP 8.0 with MySQL 5.6	1m 47s
test / Functional - WP trunk on PHP 8.1 with MySQL 8.0	1m 16s
test / Functional - WP trunk on PHP 8.2 with MySQL 8.0	1m 18s
test / Functional - WP trunk on PHP 8.3 with MySQL 8.0	1m 27s
test / Functional - WP trunk on PHP 8.2 with SQLite	1m 10s
test / Functional - WP trunk on PHP 8.3 with SQLite	55s
test / Functional - WP trunk on PHP nightly with MySQL 8.0	1m 30s
test / Functional - WP trunk on PHP nightly with SQLite	59s
	20m 2s

Provide feedback