SITL: fix json airspeed #39962

Job	Run time
build (stm32f7, chibios, 10)	6m 5s
build (stm32h7, chibios, 10)	5m 48s
build (fmuv2-plane, chibios, 10)	4m 6s
build (periph-build, chibios, 10)	5m 39s
build (iofirmware, chibios, 10)	4m 2s
build (CubeOrange-bootloader, chibios, 10)	3m 6s
build (fmuv3-bootloader, chibios, 10)	3m 13s
build (revo-bootloader, chibios, 10)	3m 16s
build (stm32h7-debug, chibios, 10)	9m 23s
build (fmuv3, chibios, 10)	7m 33s
build (revo-mini, chibios, 10)	6m 19s
build (MatekF405-Wing, chibios, 10)	6m 46s
build (CubeOrange-ODID, chibios, 10)	4m 49s
build (CubeRedPrimary-bootloader, chibios, 10)	3m 3s
build (configure-all, chibios, 10)	12m 56s
build (build-options-defaults-test, chibios, 10)	9m 57s
build (signing, chibios, 10)	4m 45s
build (CubeOrange-PPP, chibios, 10)	4m 13s
build (SOHW, chibios, 10)	5m 33s
build (Pixhawk6X-PPPGW, chibios, 10)	3m 40s
build (new-check, chibios, 10)	6m 29s
	2h 0m 41s

Provide feedback