feat: save cache on job failure

[LNSD]

Context

As stated by @TimJentzsch in #14:

Unfortunately, the cache action only saves the cache if the workflow succeeded.
For cargo, this doesn't make much sense as e.g. a failing test doesn't influence the build artifacts.

The difficulty here is that the action does not provide any option to configure this.
We could use the actions/cache@main/save action to manually save the cache, but then we can't put it at the end of the job, since compose actions don't have a way to set a post action to my knowledge...

Proposed Solution

The actions/cache action was upgraded to v4 in the previous pull request. This update brought forth the save-always option, allowing the cache to be preserved even in the event of a preceding step failure.

To align with this enhancement, I am introducing the save-always action input to the cargo-cache action and cascading it to the internal actions/cache step. If the save-always action parameter is not set, by default, the cache will always be saved.

This PR resolves #14

[TimJentzsch]

Sounds good, thank you!

[TimJentzsch]

Actually, Alice is recovering from the Bevy release so I'll just go ahead and merge this

[TimJentzsch]

@LNSD Released as v1.2.0 and v1!