[BUG] Multi-task learning metrics inconsistent due to a mismatch or tasks and metrics order

[gabrielspmoreira]

Bug description

When training multi-task learning models the tasks metrics names values are some times shuffled
For example

metrics == {
"conversion/binary_classification_task_auc": <click_auc_result>,
"click/binary_classification_task_auc": <conversion_auc_result>
} 

Steps/Code to reproduce bug

The issue happens when the order with which PredictionTask are created do not match their task names sorted order.
In the above example, the error occurs if the conversion BinaryClassificationTask is created before the click one, but the opposite does not raise an error.

Expected behavior

Each metric should contain its own value

Environment details

• Merlin version: 22.09
• Tensorflow version: 2.9.1