Remove warnings, errors during host tests in CI

[earlephilhower]

Debug strings often included format parameters which did not exactly match
the passed in format parameters, resulting in warnings in the host test build
process like

/home/runner/work/Arduino/Arduino/libraries/ESP8266WiFi/src/ESP8266WiFiAP.cpp:107:20: warning: format ‘%u’ expects argument of type ‘unsigned int’, but argument 3 has type ‘size_t’ {aka ‘long unsigned int’} [-Wformat=]
  107 |         DEBUG_WIFI("[AP] SSID length %u, too long or missing!\n", ssid_len);
      |                                                                   ~~~~~~~~
      |                                                                   |
      |                                                                   size_t {aka long unsigned int}

Fix by applying casting or PRxxx macros as appropriate.

Also, fix one debug message which was trying to use a String as a char *:

/home/runner/work/Arduino/Arduino/libraries/ESP8266WiFi/src/ESP8266WiFiMulti.cpp: In member function ‘wl_status_t ESP8266WiFiMulti::connectWiFiMulti(uint32_t)’:
/home/runner/work/Arduino/Arduino/libraries/ESP8266WiFi/src/ESP8266WiFiMulti.cpp:331:34: warning: format ‘%s’ expects argument of type ‘char*’, but argument 3 has type ‘String’ [-Wformat=]
  331 |                 DEBUG_WIFI_MULTI("[WIFIM] Connecting %s\n", ssid);

[d-a-v]

Thanks !
Compilation on host is now clean !
🎉