tests/pkg_cc25519: increase timeout for arduino-mega2560
tests/pkg_cc25519: increase timeout for arduino-mega2560

`arduino-mega2560` finishes the test in 170 seconds so set a bigger timeout.

mfrey/RIOT,authmillenon/RIOT,OTAkeys/RIOT,aeneby/RIOT,x3ro/RIOT,rfuentess/RIOT,mtausig/RIOT,mtausig/RIOT,miri64/RIOT,authmillenon/RIOT,jasonatran/RIOT,aeneby/RIOT,OTAkeys/RIOT,mfrey/RIOT,yogo1212/RIOT,ant9000/RIOT,ant9000/RIOT,rfuentess/RIOT,basilfx/RIOT,toonst/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,cladmi/RIOT,smlng/RIOT,kYc0o/RIOT,authmillenon/RIOT,josephnoir/RIOT,toonst/RIOT,x3ro/RIOT,cladmi/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,smlng/RIOT,kaspar030/RIOT,x3ro/RIOT,OlegHahm/RIOT,kYc0o/RIOT,kYc0o/RIOT,josephnoir/RIOT,kaspar030/RIOT,kaspar030/RIOT,jasonatran/RIOT,kYc0o/RIOT,yogo1212/RIOT,smlng/RIOT,cladmi/RIOT,smlng/RIOT,ant9000/RIOT,kaspar030/RIOT,josephnoir/RIOT,authmillenon/RIOT,authmillenon/RIOT,miri64/RIOT,authmillenon/RIOT,aeneby/RIOT,toonst/RIOT,mtausig/RIOT,OTAkeys/RIOT,yogo1212/RIOT,miri64/RIOT,miri64/RIOT,RIOT-OS/RIOT,toonst/RIOT,mfrey/RIOT,yogo1212/RIOT,OTAkeys/RIOT,smlng/RIOT,josephnoir/RIOT,rfuentess/RIOT,kaspar030/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,aeneby/RIOT,yogo1212/RIOT,josephnoir/RIOT,ant9000/RIOT,ant9000/RIOT,basilfx/RIOT,x3ro/RIOT,cladmi/RIOT,toonst/RIOT,mfrey/RIOT,basilfx/RIOT,OlegHahm/RIOT,basilfx/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,mtausig/RIOT,kYc0o/RIOT,x3ro/RIOT,mtausig/RIOT,rfuentess/RIOT,miri64/RIOT,rfuentess/RIOT,mfrey/RIOT,cladmi/RIOT,yogo1212/RIOT,jasonatran/RIOT,aeneby/RIOT,basilfx/RIOT,jasonatran/RIOT