[model:bugtype] ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

[jpangas]

Another bug to be looked at.

File "/usr/local/lib/python3.10/site-packages/bugbug/model.py", line 546, in <genexpr>
    classified_num = sum(1 for v in y_pred_filter if v != "__NOT_CLASSIFIED__")

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

Originally posted by @jpangas in #3958 (comment)

[jpangas]

We are counting classified_num for the multi-label cases. The current way works for the binary-label case only.
Proposed:
classified_num would be len(classified_indices) for multi-label cases.

bugbug/bugbug/model.py

Lines 546 to 547 in 0bcedc3

	classified_num = sum(1 for v in y_pred_filter if v != "__NOT_CLASSIFIED__")