When test crashes, the report about this is written to output encoded in UTF-16 (or UCS2). In other words, ASCII characters are intermixed with null bytes. The problem is that while the browser simply do not show null bytes, so you can read the message, you cannot copy it, because the content of clipboard is truncated at null bytes.

See for example https://github.com/python/cpython/actions/runs/6094370280/job/16535778004#step:5:1112

A�s�s�e�r�t�i�o�n� �f�a�i�l�e�d�:� �t�s�t�a�t�e�_�i�s�_�a�l�i�v�e�(�t�s�t�a�t�e�)� �&�&� �!�t�s�t�a�t�e�-�>�_�s�t�a�t�u�s�.�b�o�u�n�d�,� �f�i�l�e� �D�:�\�a�\�c�p�y�t�h�o�n�\�c�p�y�t�h�o�n�\�P�y�t�h�o�n�\�p�y�s�t�a�t�e�.�c�,� �l�i�n�e� �2�4�5�

It was copied from the raw logs view. In normal view you do not see any �, but you cannot copy this line past the first A.