Update to node20 and use package instead of node_modules & bugfixes

[humble-barnacle001]

Hi, I wanted to improve certain things and make some bugfixes:

• use a package instead of node_modules folder as per GitHub recommendations
• upgrade to node 20 runner from node 16 to resolve actions warning
• fix a typo in variable in index.js
• use .env file instead of modifying test_config