ci: set cache scope

[beniaminopozzan]

No description provided.

[mrpollo]

if this works you are my hero!

[beniaminopozzan]

@mrpollo

• first build -> no cache (makes sense as scope changed)
• second build where only one file was added -> cache was used! action time dropped to 5 min
• third build with rebase and the file was removed -> cache was used! action time agan 5 min

however, this other pr: #32 which is made on top of this one did not used the cache at all https://github.com/Dronecode/roscon-25-workshop/actions/runs/18667702426 (I cancelled the workflow when I saw no cache being used)

could you still approve please? Once the change is in main it might behave properly even for other PRs, thanks!

(if merging, please quash and merge 🙇🏻 )

[mrpollo]

hero status confirmed

[mrpollo]

i didnt read the squash part sorry lol

[beniaminopozzan]

@mrpollo I'm not 100% convinced it worked as intended:
https://github.com/Dronecode/roscon-25-workshop/actions/runs/18668707616
the post merge action did not use any cache at all

[beniaminopozzan]

tested with a few other PRs and the cache is not invalidated anymore :)

interestingly, when merging the RPs into main I would have expected to cache all layers from the previous built.
For example, for the PR #32, the last action to run on the pr sync event is https://github.com/Dronecode/roscon-25-workshop/actions/runs/18679620637. That action built the image and pushed the cache.
The RP was then closed and the branch merged, which triggered https://github.com/Dronecode/roscon-25-workshop/actions/runs/18680298157. This action used some cache for both arm64 and amd64 which is good, but it did not used the cache for ALL layers. I would have expected it to retrieve from the cache all layers