Fix build badge

Not sure why this no longer works, but changing it to use the filename instead of the action name seems to fix it.

Author: dmadison

README.md

@@ -1,5 +1,5 @@
 # Teensy XInput USB Mode
-[![Build Status](https://github.com/dmadison/ArduinoXInput_Teensy/workflows/build/badge.svg?branch=master)](https://github.com/dmadison/ArduinoXInput_Teensy/actions?query=workflow%3Abuild)
+[![Build Status](https://github.com/dmadison/ArduinoXInput_Teensy/actions/workflows/ci.yml/badge.svg?branch=master)](https://github.com/dmadison/ArduinoXInput_Teensy/actions?query=workflow%3Abuild)
 
 The files in this repository will add an additional USB mode ("XInput") to your Teensy board, allowing it to emulate an Xbox gamepad.