Add Fluff M0 to boards

Author: deshipu

.github/workflows/build.yml

@@ -177,6 +177,7 @@ jobs:
         - "feather_nrf52840_express"
         - "feather_radiofruit_zigbee"
         - "feather_stm32f405_express"
+        - "fluff_m0"
         - "gemma_m0"
         - "grandcentral_m4_express"
         - "hallowing_m0_express"