Adds an input that borrows the `save-always` input from [v4 of `actions/cache`][0], which will run the post step to save the cache even if a failure occurs. Using the added `cache-save-always` input saves the cache when a build fails, which will speed up subsequent runs which restore the partial build. This comes at the cost of requiring a build when there is an exact `key` match, since the cache from a failed build will have the same `key` as a completed build.

[0]: https://github.com/actions/cache/tree/main#v4

Saves the set of build artifacts after a build failure with a `-partial` suffix on the cache key. A full cache-hit will therefore only occur when restoring the cache saved after a successful build, allowing for the subsequent `stack build` and cache-save steps to be skipped.

Status check functions can only be used in `if` conditionals, so the use of a cache key suffix needs to be determined in a conditionally-run step.

This reverts commit dd40c85.

This reverts commit 629a6a9.

Checks that the workflow has not been cancelled (i.e., is succeeding or failed) and that `cache-save-always: true` when building and saving the cache. This extends the existing conditional on the `cache-hit` outputs, making the previously-implied `success()` check explicit.

When `cache-save-always: false`, the default behavior is unchanged for the action: steps either no-op if a cache-hit occurred, or build and save otherwise.

When `cache-save-always: true`, a building and saving the cache occurs on success or failure.