Add support for restoring from partial cache match

[artuross]

Description:
Currently, it seems that this action only restores cache if the cache key is matched exactly (go.mod and go.sum haven't changed).

Justification:
Typically, when updating dependencies, only some dependencies will be updated. With current version, it means that whenever a dependency is updated, the cache is not used and therefore all packages must be fetched. In my view, this is suboptimal.

I think there should be a setting to enable this behavior.

Are you willing to submit a PR?
Yes.

[dusan-trickovic]

Hello, @artuross ! Thank you for the suggestion, we will investigate it :)