Fix GitHub Actions warnings in "Verify" workflow

[eddybrando]

Feature description

The "Verify" workflow outputs 2 warnings in the "Test" job:

• Use of a deprecated Node.js version (v12)
• Use of a deprecated command (set-output)

We should make the necessary changes to fix them.

Example

Source: https://github.com/Qiskit/qiskit.org/actions/runs/7388048753

Additional context

No response