Suboptimal CI Caching
You need to know beforehand if you have a 100% cache hit (which also means to them that you are not going to make any changes to it). If it's not a cache hit it doesn't download anything. So either it downloads and it skips uploading or vice versa. This is pretty pointless and they need to fix it: https://github.com/actions/cache/issues/106
Unblocking because this can still be done without them changing anything.
I'll keep this open as a tracking issue for eventually improving this. The current solution is still far from optimal.
I don't think the CI times are that bad. They are mostly dominated by building the Rust code, but caching Rust's target folder usually mostly just slows things down (uploading / downloading it). So I don't think we can do much here.