Deprecation warning for Node 16

[JstnMcBrd]

https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/#what-you-need-to-do

https://github.com/pauldraper/workflow-dispatch/blob/main/action.yml#L37

  runs:
-   using: node16
+   using: node20
    main: workflow-dispatch/dist/main.js

Should probably bump a major version to pauldraper/workflow-dispatch@v2 as well.