Immunohistochemical assessment of the diagnostic utility of <scp>PD</scp>‐L1: a preliminary analysis of anti‐<scp>PD</scp>‐L1 antibody (<scp>SP</scp>142) for lymphoproliferative diseases with tumour and non‐malignant Hodgkin–Reed‐Sternberg (<scp>HRS</scp>)‐like cells