TypeScript

You defined a Composite run steps action instead of a JavaScript action.

See explanation of action types.

If you look at this TypeScript action template, it has the dist folder checked in and refers to it in its action.yaml in the property runs.main.

This means you should compile your TypeScript action locally and check in the dist folder. It also says to use ncc to compile to a single file. As described here.

name: 'Your name here'
description: 'Provide a description here'
author: 'Your name or organization here'
inputs:
  milliseconds: # change this
    required: true
    description: 'input description here'
    default: 'default value if applicable'
runs:
  using: 'node12'
  main: 'dist/index.js'