chore: Update actions/cache to v4.2.1

[lym953]

Motivation

The workflow monitor_api_integration_test.yml failed for the last run. The Cache Node Modules step prints:

Cache not found for input keys: Linux-modules-b96127d594499a9474c30b928babfc88ad64779bfcb698c950c857393d628255

Investigation

The actions/cache action repo announced: Deprecation Notice - Upgrade to latest before February 1st 2025

What does this PR do?

Update all references of actions/cache from v3 to latest (v4.2.1)

Testing Guidelines

Run the workflow and it succeeded. https://github.com/DataDog/serverless-plugin-datadog/actions/runs/13416437717

Additional Notes

Types of changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog