refactor: minor changes follows #1348

[SukkaW]

Description:

The PR follows #1348 with a bugfix and a very slight performance improvement.

• Only enable package cache when the cache feature is available
  • In Enhance caching in setup-node with automatic package manager detection #1348 new package-manager-cache logic is not guarded by isCacheFeatureAvailable(), the PR fixes this.
• Don't read package.json if the previous version's cache config is used
  • We don't have to determine the package manager if the user has explicitly specified which package manager to use, which improves performance a little.

Related issue:

Check list:

• Mark if documentation changes are required.
• Mark if tests were added or updated to cover the changes.

[Copilot]

Pull Request Overview

This PR refactors the caching logic in the main setup-node workflow to improve performance and properly guard cache functionality. The changes ensure package cache is only enabled when the cache feature is available and avoid unnecessary package.json reads when the cache field is explicitly specified.

• Only enable package manager caching when the cache feature is available by wrapping logic with isCacheFeatureAvailable()
• Defer reading package.json until needed by moving getNameFromPackageManagerField() call inside conditional blocks
• Restructure cache logic to prioritize explicit cache input over automatic package manager detection

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[SukkaW]

cc @priya-kinthali @aparnajyothi-y @mahabaleshwars @HarithaVattikuti