Remove `phpcs-diff` workaround

[tomalec]

UserDeveloper story

As the github-actions/actions/phpcs-diff/action.yml developer, I want to maintain the least amount of code possible.

Is your feature request related to a problem?

We used to have a problem that was worked around by #27
that originates in exussum12/coverageChecker#72, and was already fixed at source.

How to reproduce the problem

Run phpcs-diff action when no changes are made.

Describe the solution you'd like

Remove no longer needed code, once the https://github.com/exussum12/coverageChecker >1.0.2 is released

Describe alternatives you've considered

Technical

Figma link

n/a

Acceptance criteria

Unknowns

Out of bounds/rabbit holes

Event tracking

n/a