Improve caching in GitLab Pipeline

[niclasheinz]

Based on #7990 I have improved the caching in GitLab pipelines. Now the .cache folder is stored in the cache.

[squidfunk]

Thanks for the PR! I'm looping in @kamilkrzyskow here, maybe he can comment if he has the time. Historically, correct caching has been a tricky topic, so we need to get this right. I currently do not have the time to properly review this, but maybe we can reach a consensus in a discussion here, so we can be sure that it improves the situation. Prior art:

• Update cache key creation to use date suffix #5463
• Revert cache to use github.ref instead of github.sha #5460
• Fix GitHub Action caching methodology #5448

[squidfunk]

Ah wait, I've mistaken this for our workflow 🤦‍♂️ Never mind, sorry for the noise. I guess it's good to merge.

[kamilkrzyskow]

LGTM, I asked Deepseek to provide an example of caching a .cache directory in GitLab CI, and it mentioned that there is the policy option which is set to pull-push by default. So despite the cache key being static in this case it will always download and upload the given path assuring the proper cache updates, this is what we want.

It works differently than in GitHub, where a primary cache key (exact match) doesn't warrant a upload with updated files, which lead me down the rabbit hole of using time 😅

[squidfunk]

@kamilkrzyskow Thanks! Note that I've mistaken this for our workflow, which we need to revisit at some point, but no hurry. This is why I tagged you in the first place, which I hope was okay.