Bump outdated GitHub Actions to v4

[mr-raj12]

Description

Update all GitHub Actions that are still pinned to v3 (Node.js 16, EOL since September 2023) to v4 (Node.js 20). Also standardize codecov/codecov-action to v4 across both unit and integration test jobs.

Changes across 3 files (6 edits):

File	Action	Change
.github/workflows/test.yml	actions/checkout	v3 → v4 (4 occurrences: lint, prepare-matrix, test-unit, test-integration)
.github/workflows/test.yml	codecov/codecov-action	v3 → v4 (unit test job, integration was already v4)
.github/workflows/build-macos.yml	actions/checkout	v3 → v4
.github/actions/setup/action.yml	actions/cache	v3 → v4

Related Issue

Closes #2376

Motivation and Context

GitHub has been issuing deprecation warnings for actions running on Node.js 16. The v3 tags of actions/checkout, actions/cache, and codecov/codecov-action all use Node.js 16. Bumping to v4 moves to Node.js 20 and eliminates these warnings. The codecov version was also inconsistent between the unit test job (v3) and integration test job (v4), which is now standardized.

How Has This Been Tested?

• These are CI-only configuration changes (YAML version tag bumps) with no functional code changes
• The PR's own CI run will validate that all updated actions work correctly (lint, unit tests, integration tests)
• No local testing is applicable since these are GitHub Actions runner changes

Screenshots (if appropriate):

N/A — No visual changes

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have read the CONTRIBUTING guide.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

I provide my contribution under the terms of the license of this repository and I affirm the Developer Certificate of Origin.