Severe COVID-19 Infection in Patients with Chronic Lymphocytic Leukemia or Indolent B-Cell Non-Hodgkin Lymphoma Who Received Pre-Exposure Prophylaxis with Tixagevimab and Cilgavimab in Italy: Preliminary Results of the Observational Study By the Gimema Working Party on Chronic Lymphoproliferative Disorders and By the Fondazione Italiana Linfomi