I hate the word 'nitpick' (bad experience with small insects - thinking about nits makes me itch), but I don't know any other word for these "small, trivial, but necessary changes." Does anyone have alternative words they use in reviews instead?
To be clear, the (American) dictionary definition of nit-picking is "minute and usually unjustified criticism." In other words, this is definitely not a positive thing to do, which is why this word has such strong negative connotations. Who wants to be nitpicked?
Nit-picking is not a "necessary" change, which is what makes it an exercise in finding the tiniest of fungus flies lurking in a proposed change. "I don't really want to think too hard about what you're proposing, or what your pull request contains, so here's a nit I noticed while examining the bike shed in front of your nuclear plant. #didmyjobboss"
I don't know what a trivial but necessary change is, but that's certainly not a minute criticism.
This is very possibly a team culture thing, though. We all know that the code is what matters, and we are all studiously not letting our egos intervene, but we can help each other not get too attached by deflecting the blame onto the reviewer rather than the author in this tiny way.
I use nit, but usually for not necessary changes. If my only reviews on a change are nits, I leave the comments but give the greenlight for merging the change (at which point the author may ignore the nits or address them at their discretion)