subpaths should be quoted to prevent nonsensical messages

[jsoref]

https://github.com/nektos/act/blob/324bab61f056e7e103b142b4c2f8b3b34421d764/pkg/runner/action_cache.go#L135

• #2752 shows that path '' is quoted, subpaths should be quoted for the same reasons (it's confusing when they're empty, and it's confusing when they have spaces in their names)