The `npm_config_cache` env, if set, will have highest priority, and harder to change.
One way to un-set this is add a global workflow env, like:
```
env:
npm_config_cache: ''
```
This commit change the cache config to use `npm config set cache $CachePath --global`,
which should save the path under the global npmrc at: `C:\npm\prefix\etc\npmrc`,
and allow easier later reset with user/repo level `.npmrc` files.
For the record, my usage is to unify all platform's npm cache to `~/.npm/`,
then use the same cache action config on all platform to cache the folder.
