Guess I haven't had enough coffee -- I'm struggling to remember the joke in which the punchline is the professional telling the client something like "You're not paying me to do [one simple/small thing], but for the years of experience it takes to know that [it's that one simple thing]".

The problem with trying to charge for programming work is that so much non-trivial work can be summed up as a few keystrokes, or an addition of a single line, or even producing less code (by deletion/refactoring). That said, I don't understand why your boss thought this subterfuge was necessary. If the client is non-technical enough to approve 8 hours of billing for something that takes 5 minutes to fix, how is that client competent enough to look through the git history to know that it was only 5 minutes of work?