update code coverage workflow to use actions with node 20 support

[onkarvhanumante]

• As of now, warning related to node 16 usage were seen on prebid/prebid-server for code coverage workflow.
  

• As per, https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20 Node 16 has reached its end of life and it is recommended to transition to use Node 20 by Spring 2024.

• PR makes changes in code coverage workflow to use actions with node 20 support.

• Tested by running code coverage workflow on forked repo.
  https://github.com/onkarvhanumante/prebid-server/actions/runs/7811209264
  

[AlexBVolcy]

Just presenting some additional context regarding GitHub Actions, and the changes made in this PR.

Here are all workflow action uses that were updated in this PR, and their related releases that denote the update from node16 -> node 20

setup-go v5
checkout v4
github-script v7

What setup-go does:

• Installs Go and Version
• Sets up environment variables (GOROOT, GOPATH)

What checkout does:

• Checks out the relevant branch

What github-script does:

• Allows a workflow to run a custom JavaScript script

How Node.js is related
Node.js isn't directly utilized by setup-go and checkout, but potentially it's used behind the scenes to handle relevant action tasks

Node.js is however directly related to github-script, with the custom JavaScript code provided from the action is run in a Node.js enviornment.

[onkarvhanumante]

** Node.js is related** Node.js isn't directly utilized by setup-go and checkout, but potentially it's used behind the scenes to handle relevant action tasks

Node.js is however directly related to

thanks @AlexBVolcy