fix: signature of set_subkey() #30

Job	Run time
Build Test (WiFi): esp8266:generic	1m 42s
Build Test (Ethernet): avr:uno	43s
Build Test (WiFi): esp32:esp32	1m 50s
Build Test (ETH): esp32:esp32	2m 3s
Build Test (Ethernet): megaavr:uno2018	50s
Build Test (WiFi): esp32:esp32s3	1m 50s
Build Test (ETH): esp32:esp32s3	2m 4s
Build Test (Ethernet): samd:mkrvidor4000	1m 3s
Build Test (ETH): esp32:esp32c3	1m 57s
Build Test (Ethernet): samd:mkrwifi1010	1m 4s
Build Test (WiFi): esp32:esp32c3	1m 46s
Build Test (WiFiNINA): megaavr:uno2018	47s
Build Test (Ethernet): samd:mkr1000	1m 3s
Build Test (WiFi): rp2040:rpipicow	2m 16s
Build Test (WiFiNINA): samd:mkrvidor4000	1m 9s
Build Test (Ethernet): samd:nano_33_iot	1m 10s
Build Test (WiFiNINA): samd:mkrwifi1010	1m 4s
Build Test (Ethernet): esp8266:generic	1m 6s
Build Test (Ethernet): esp32:esp32	1m 26s
Build Test (WiFiNINA): samd:nano_33_iot	1m 13s
Build Test (Ethernet): esp32:esp32s3	1m 20s
Build Test (Ethernet): esp32:esp32c3	1m 16s
Build Test (Ethernet): rp2040:rpipicow	58s
	31m 40s

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