fix: correct ADVERT_NAME for Generic ESPNow room server (was 'Heltec Room')

env:Generic_ESPNOW_room_svr was using 'Heltec Room' as ADVERT_NAME,
causing Generic ESPNow room server nodes to advertise with the wrong
device name on the mesh.

variants/generic_espnow/platformio.ini

@@ -69,7 +69,7 @@ lib_deps =
 extends = Generic_ESPNOW
 build_flags =
   ${Generic_ESPNOW.build_flags}
-  -D ADVERT_NAME='"Heltec Room"'
+  -D ADVERT_NAME='"Generic ESPNow Room"'
   -D ADVERT_LAT=0.0
   -D ADVERT_LON=0.0
   -D ADMIN_PASSWORD='"password"'