Update onekey proton_c readme (#9758)

A3 won't work. The code says A1 and A2 and it works. prints out an "a"

keyboards/handwired/onekey/proton_c/readme.md

@@ -1,3 +1,3 @@
 # Proton C onekey
 
-To trigger keypress, short together pins *A3* and *A2*.
+To trigger keypress, short together pins *A1* and *A2*.