[code coverage] compares current and base branch code cov %

[kennethrioja]

Summary of changes

• test.yml: while testing the current branch, it keeps now the total code coverage in %, as well as code coverage per changed file. If there are modification on .rb files, it also runs the entire test suite in the base branch. Then it compares code coverage difference between the two branches:
  • if there is an improvement or none, it passes
  • if there is a decrease in code coverage %, it fails

Motivation and context

This follows up Finn's comment : #1149 (comment)

testing, I think it would be nice to set-up a GH Action that fails if the code coverage % decreases in a PR.

Checklist

• I have read and followed the CONTRIBUTING guide.
• I confirm that I have the authority necessary to make this contribution on behalf of its copyright owner and agree
  to license it to the TeSS codebase under the
  BSD license.

DEPRECATED

Feature: It used to write a message on the PR, see screenshot, but that was when testing on my personal repo, where I had the authority to write, when writing in ElixirTeSS:master, we need to have a secret key/variable (even when permissions pull-request: write)... for now let's keep it simple

Screenshots

[kennethrioja]

Must rewrite it in another action... wip