In effect you can do the same thing better by using a cryptocurrency with cheap transactions, e.g. Bitcoin Cash's Memo.cash. This way git hosts are compensated while at the same time making it too costly to spam.

Longer packfile creation processes will require a greater transaction fee or otherwise be ignored based on heuristics created by the client. This will prevent infinite CPU building packfiles issues in addition to fair compensation for increased computation cost. All while the miner is incentivized to minimize the time to be able to reap that block reward in the context of market competition.