Covid cannot easily survive in 40°C heat!
Interesting study: https://aip.scitation.org/doi/figure/10.1063/5.0024272
The diagram shows that after 3s with 40°C and 50% humidity the contaminated respiratory droplets are nearly gone.
Together with the minimum distance of 1,5m in class between yogis hot yoga is safe. And if you know the classic hot yoga sequence: We do Pranayama and Kapalbhati with closed mouth (breathing through the nose only) to further minimise possible transmission.