WiFi: fix memory leak in scanNetworks() #1340

Job	Run time
compile-examples (arduino:mbed:nanorp2040connect, nanorp2040connect)	12m 30s
compile-examples (arduino:mbed:envie_m7:target_core=cm4, envie_m7_core_cm4)	5m 52s
compile-examples (arduino:mbed:giga, giga)	26m 30s
compile-examples (arduino:mbed:nano33ble, nano33ble)	7m 11s
compile-examples (arduino:mbed:opta, opta)	18m 6s
compile-examples (arduino:mbed:envie_m7, envie_m7)	27m 10s
compile-examples (arduino:mbed:nicla_voice, nicla_voice)	5m 7s
compile-examples (arduino:mbed:nicla_sense, nicla_sense)	12m 27s
compile-examples (arduino:mbed:edge_control, edge_control)	5m 15s
compile-examples (arduino:mbed:nicla_vision, nicla_vision)	15m 24s
	2h 15m 32s

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