disable CGO in the release CI as is not needed by this tool

[umbynos]

Should solve arduino/arduino-cli#1652

[cmaglie]

It builds, then it must be good :-)

[umbynos]

On armv7:
v1.0.8:

root@d32f9de3786d:/# file ~/.arduino15/packages/builtin/tools/mdns-discovery/1.0.8/mdns-discovery 
/root/.arduino15/packages/builtin/tools/mdns-discovery/1.0.8/mdns-discovery: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.3, Go BuildID=KGavsUH2x_O95RJQCPTb/UBSfk0HX-mtUV2X6fNw4/rIZZ7znSQLYGUPErktLe/M0Qow1viniMr_CipPEUt, not stripped
root@d32f9de3786d:/# ~/.arduino15/packages/builtin/tools/mdns-discovery/1.0.8/mdns-discovery 
qemu-arm: Could not open '/lib/ld-linux.so.3': No such file or directory

v1.0.9-rc1 (version with this change):

mdns-discovery_linux_arm_6/mdns-discovery: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), statically linked, Go BuildID=PuhFKqXIvBtKMe8klM43/A5QVowcfZZlIheAniDC9/CFRI7H4ZIyWoLazVvjOc/kqHSN4OEhL2Nh7G69RdK, not stripped
root@d32f9de3786d:/tmp# ./mdns-discovery_linux_arm_6/mdns-discovery 
HELLO 1 "cli"
{
  "eventType": "hello",
  "message": "OK",
  "protocolVersion": 1
}
QUIT
{
  "eventType": "quit",
  "message": "OK"
}