There is no fixed answer to "how many revives is too many" because how a character's resurrection comes across to the reader is entirely dependent on context. If the revive system is just there to allow you to kill of and resurrect characters, thus eliminating any real danger from your story, ONCE is too many. But if the revive system is part of a larger world building system, and there are still things at stake, the answer is "as many times as you feel necessary."
As other answers pointed out, it is all dependent on what the consequences are for the characters, and the way that the resurrection is worked into the plot. Others have mentioned "Edge of Tomorrow" as a good example of seemingly infinite revives that don't deminish (and in this case are actually a keystone to the plot of) the story. I would add the netflix show "Altered Carbon" as another example. In that universe, normal death isn't necessarily permanent, as you can just be rebooted (but there are a lot of different factors that affect whether you will be or not, such as economic status, and also some consequences even if you are, such as potentially having to adjust to a new body. all these things help keep the whole narrative engaging.) Additionally, there is a form a death still that IS permanent, because if the part of you that is used to reboot you is lost, you're gone for good. So in this case there is a system that allows for supposedly infinite resurrections, but there is still a lot at stake and still a risk of permanent death.
To summarize: Context is everything. Set things up wrong, and you'll lose your reader's investment in the story. Set it up well, and you can resurrect as many people as you like as often as you need without losing the reader, because you have other things at stake to keep them interested.