Upgrade all dependencies and modernize setup

[f:4h]

Author: stefanmaric

.eslintignore

@@ -0,0 +1 @@
+save-exact=true

.eslintrc.json

@@ -1 +1 @@
-18
+20

.npmrc

@@ -2,6 +2,8 @@ import * as process from 'node:process'
 import * as cp from 'node:child_process'
 import * as path from 'node:path'
 
+import { test, expect } from 'vitest'
+
 const REQUIRED_VARIABLES = [
   'INPUT_GITHUB_TOKEN',
   'SLACKSYNC_CHANNEL',

.nvmrc

@@ -14,6 +14,6 @@ inputs:
     default: ${{ github.token }} # same as ${{ secrets.GITHUB_TOKEN }}
     required: true
 runs:
-  using: 'node16'
-  main: 'dist/main.js'
-  post: 'dist/main.js'
+  using: 'node20'
+  main: 'dist/main.cjs'
+  post: 'dist/main.cjs'