The bug

When a function runs /return fail the feedback of the /function command is identical to the feedback of a function running /return 0.

Steps to reproduce

1. Create a function (called return:0) /return 0
2. Create a function (called return:fail) return fail
3. Turn command feedback on. /gamerule sendCommandFeedback true
4. Run the first function via chat. /function return:0
   -> "Function return:0 returned 0"
5. Run the second function via chat. /function return:fail
   -> "Function return:fail returned 0"

Expected result

"Function return:fail returned failure" or an alike message.
Returning fail is different from returning 0 as returning 0 has a success of 1 and passes execute if function while fail has a success of 0 and fails execute if function