GCS_MAVLink: emit warning when MISSION_SET_CURRENT received #45181

Job	Run time
build (stm32f7, chibios, 10)	4m 3s
build (stm32h7, chibios, 10)	3m 48s
build (fmuv2-plane, chibios, 10)	1m 51s
build (periph-build, chibios, 10)	5m 3s
build (iofirmware, chibios, 10)	1m 52s
build (CubeOrange-bootloader, chibios, 10)	50s
build (fmuv3-bootloader, chibios, 10)	1m 8s
build (revo-bootloader, chibios, 10)	1m 12s
build (stm32h7-debug, chibios, 10)	2m 19s
build (fmuv3, chibios, 10)	5m 38s
build (revo-mini, chibios, 10)	4m 22s
build (MatekF405-Wing, chibios, 10)	4m 49s
build (CubeOrange-ODID, chibios, 10)	2m 37s
build (CubeRedPrimary-bootloader, chibios, 10)	55s
build (configure-all, chibios, 10)	11m 36s
build (build-options-defaults-test, chibios, 10)	7m 39s
build (signing, chibios, 10)	3m 5s
build (CubeOrange-PPP, chibios, 10)	2m 28s
build (CubeRed-EKF2, chibios, 10)	2m 27s
build (SOHW, chibios, 10)	3m 57s
build (Pixhawk6X-PPPGW, chibios, 10)	1m 37s
build (new-check, chibios, 10)	4m 53s
	1h 18m 9s

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