[ACS-10385] Fix missing "WWW-Authenticate" header 9.N backport

[cezary-witkowski]

Backporting #72

[Copilot]

Pull Request Overview

This PR fixes a missing "WWW-Authenticate" header issue by correcting the order of operations in an authentication error response and updates GitHub Actions cache dependencies to a more recent version.

• Moves the "WWW-Authenticate" header setting before the error response is sent to ensure proper HTTP authentication flow
• Updates GitHub Actions cache action from v1 to v4 across multiple workflow jobs

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
FeedController.java	Reorders header setting to occur before sending the HTTP error response
build.yml	Updates cache action version from v1 to v4 in three workflow jobs

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}