scan-ref doesn't work when using filesystem instead of fs

[kderck]

Hello Aqua Security, if you have a scan-type: filesystem instead of scan-type: fs the action will error with FATAL Require at least 1 argument if you have specified scan-ref: . However, this shouldn't be a problem as fs is an alias of filesystem

 - name: Scan Dependencies with Trivy
   uses: aquasecurity/trivy-action@master
   with:
        scan-type: filesystem
        scan-ref: .

[kderck]

I've noticed this issue is caused by there being no catching case in entrypoint.sh and not scan-ref itself.