bump: run with node20 (#25)

Node.js 16 actions are deprecated. Please update the following actions
to use Node.js 20: oras-project/setup-oras@v1.1.0. For more information
see:
https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.

Fixes #23

Signed-off-by: Lan Liang <gcslyp@gmail.com>

action.yml

@@ -22,5 +22,5 @@ inputs:
     required: false
     default: 1.1.0
 runs:
-  using: node16
-  main: dist/index.js
+  using: node20
+  main: dist/index.js