Upgrade the get-plugin-releases action to use Node.js v20

[eason9487]

Changes proposed in this Pull Request:

Part of #108

This PR upgrades the get-plugin-releases action to use Node.js v20.
In addition, it makes the action easier to develop and test.

Detailed test instructions:

1. Test the action locally
   1. Use Node.js v20
   2. cd packages/github-actions
   3. npm install
   4. node --watch actions/get-plugin-releases/src/get-plugin-releases.js
   5. There should be no output because it's changed to only perform directly when running in GitHub Actions
   6. Edit the packages/github-actions/actions/get-plugin-releases/src/get-plugin-releases.js file and save it with the following test code at the end of the file

      getPluginReleases( {
      	slug: 'wordpress',
      	numberOfReleases: 10,
      	includeRC: false,
      	includePatches: false,
      } );
      
      getPluginReleases( {
      	slug: 'woocommerce',
      	numberOfReleases: 10,
      	includeRC: true,
      	includePatches: true,
      } );

   7. There should be corresponding outputs
      
2. View a previous workflow run used v1 action
   • https://github.com/woocommerce/google-listings-and-ads/actions/runs/8652279994
   • There are warnings of using Node.js 16
     
3. View a test workflow run used updated action
   • https://github.com/eason9487/grow/actions/runs/8828174294
   • There's no more warning of using Node.js 16
     
4. View the versions output
   • https://github.com/eason9487/grow/actions/runs/8828174294/job/24236656175#step:8:1
     

[mikkamp]

Thanks for the changes, they look good to me.

I can confirm I'm getting the correct results locally. Now that we use fetch directly I also don't see any flakey results being returned. The results from a previous run and a new run look good, and I can confirm the warnings are no longer present.