Cannot export to Mahara portfolio on php8

Requirements All the tests must be done with Moodle running with PHP 8, and with the 3 branches (311, 400, master). The tests require to be able to install multiple moodle instances and setup MNet. The tests require to be able to install Mahara and setup MNet. It's important to have the apache logs at hand and also display errors enabled. To, along the whole process, verify that there isn't any serialisation problem anymore. Testing Moodle <==> Moodle SSO / roaming ( MDL-74394 ) Repeat the testing instructions of MDL-74394 Verify they pass ok and there isn't any serialisation problem in logs. Testing Moodle ==> Mahara portfolio ( MDLQA-314 ) Repeat the testing instructions of MDLQA-314 Verify they pass ok and there isn't any serialisation problem in logs. Note to the reviewers / tester: I was not sure if copying / pasting the instructions here was better, but think it's clearer if they are just referenced and the originals are not touched. Specially for future issues. If you think that it's better to have the complete versions here, I'm happy to do, just tell me.