Caching already cached artifacts

[eureka-cpu]

I noticed on my second run, after not changing any of the dependencies of my build I'm seeing some pretty long wait times for caching artifacts, which you'd think wouldn't happen since they were already cached on the previous run: https://github.com/Cloud-Scythe-Labs/cargo-reaper/actions/runs/15789495198/job/44512677100?pr=24

[eureka-cpu]

In the case linked above, it took 34mins for the magic nix cache step to complete, the previous run took ~8mins: https://github.com/Cloud-Scythe-Labs/cargo-reaper/actions/runs/15789299694/job/44512155113

[unhammer]

Similarly for my project (using @main today so I guess e994df0 )

• Without the cache, my nix build takes about 12 minutes.
• After enabling the cache, the nix build step takes 12 minutes, then 4 minutes for "Post Run the Magic Nix Cache".
• Then on the second build after enabling cache, the nix build step takes 12 minutes, then 10 minutes for "Post Run the Magic Nix Cache".

[eureka-cpu]

Yep, noticed it just seems to always cache new things even when there aren't any changes that should have made that necessary @grahamc