Flux variations of cosmic ray air showers detected by LHAASO-KM2A during a thunderstorm on June 10, 2021* * Supported in China by National Key R&D program of China (2018YFA0404201, 2018YFA0404202, 2018YFA0404203, 2018YFA0404204), NSFC (U2031101, 11475141, 12147208) and in Thailand by RTA6280002 from Thailand Science Research and Innovation