./Python/traceback.c:            write(fd, &c, 1);
./Python/traceback.c:        write(fd, "\"", 1);
./Python/traceback.c:        write(fd, "\"", 1);
./Python/traceback.c:    write(fd, "\n", 1);
./Python/traceback.c:            write(fd, "\n", 1);

Oh, I wrote these ones. It is code called by the faulthandle module, from a signal handler. So only async-safe functions can be called (no thread, no memory allocation, no lock!, etc.).

A simple fix would be to mark that we don't care if write() fails, but (void)write(fd, ...); doesn't make the warning quiet.