split workflow.yml

[MatousJobanek]

split the workflow.yml file into

• test-with-coverage.yml
• linters.yml

The main reason is that with the new configuration: pull_request_target the workflow automatically checks out the code from master and not from PR. To make it work, we need to use:

    - name: Checkout code
      uses: actions/checkout@v4
      with:
        ref: ${{github.event.pull_request.head.ref}}
        repository: ${{github.event.pull_request.head.repo.full_name}}

however, this is needed only for the tests, not for linters.

[MatousJobanek]

we could, but sometimes I get lost in the generic workflows that contain just too many actions and steps