Ignore NativeEthernet on AT90USB1286 (#19885)

.github/workflows/test-builds.yml

         - esp32
         - linux_native
         - mega2560
+        - at90usb1286_dfu
         - teensy31
         - teensy35
         - teensy41
 
         # Non-working environment tests
         #- at90usb1286_cdc
-        #- at90usb1286_dfu
         #- STM32F103CB_malyan
         #- mks_robin_mini
 

platformio.ini

 platform      = teensy
 extends       = common_avr8
 board         = at90usb1286
-lib_ignore    = ${env:common_avr8.lib_ignore} Teensy_ADC
+lib_ignore    = ${env:common_avr8.lib_ignore}, Teensy_ADC, NativeEthernet
 
 #
 # AT90USB1286 boards using DFU bootloader