[MNT] ci: Bump actions versions

[ales-erjavec]

Issue

From CI logs:

Node.js 20 actions are deprecated. The following actions are running on Node.js 20 and may not work as expected: actions/cache@v4, actions/checkout@v4, actions/setup-python@v5, codecov/codecov-action@v4. Actions will be forced to run with Node.js 24 by default starting June 16th, 2026.

Description of changes

• Bump gh actions versions to avoid Node 20 deprecation warnings in CI logs

Includes

• Code changes
• Tests
• Documentation