task_labels experience attribute type fix: now it is a list, not a set

[vlomonaco]

Hello, I found a bug in the task_incremental_benchmark generator. Even with the MNIST example in the notebook "_03benchmarks.ipynb" exp.task_labels is a set not a list as the train method expects.

I think the problem is here, where we convert the set in the list only for the task_label attribute: https://github.com/ContinualAI/avalanche/blob/0d6f7155446b2b4b25b33b8e7d21284ca8d7d06a/avalanche/benchmarks/scenarios/task_aware.py#L89-L105

The set is never converted into a list for the attribute task_labels and in in this method we use the indexing which is not supported by a set: https://github.com/ContinualAI/avalanche/blob/0d6f7155446b2b4b25b33b8e7d21284ca8d7d06a/avalanche/evaluation/metric_utils.py#L249-L275

Below you can find the small fix + an assert I added in the TaskAware tests.

[coveralls]

Pull Request Test Coverage Report for Build 9193158769

Details

• 2 of 3 (66.67%) changed or added relevant lines in 2 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage remained the same at 51.803%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tests/benchmarks/scenarios/test_task_aware.py	0	1	0.0%
<!--	Total:	2	3	66.67%	-->

Files with Coverage Reduction	New Missed Lines	%
tests/benchmarks/scenarios/test_task_aware.py	1	34.21%
<!--	Total:	1		-->

Totals
Change from base Build 9014120340:	0.0%
Covered Lines:	15082
Relevant Lines:	29114

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💛 - Coveralls