Fix security.authenticate response

[pquentin]

Server code: https://github.com/elastic/elasticsearch/blob/935384235aadf4b4227e6432e0e4894e3ec5c0a1/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/authc/Authentication.java#L802-L825

internal is only set for Cloud keys.

Initially added in #5270 but we now have YAML tests for this.

[github-actions]

Following you can find the validation changes against the target branch for the API.

API	Status	Request	Response
security.authenticate	🔴 → 🟢	30/30	25/30 → 30/30

You can validate this API yourself by using the make validate target.

[github-actions]

The backport to 9.1 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-9.1 9.1
# Navigate to the new working tree
cd .worktrees/backport-9.1
# Create a new branch
git switch --create backport-5385-to-9.1
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 68b3a3d505888db0bda68cbe4a607207236f6745
# Push it to GitHub
git push --set-upstream origin backport-5385-to-9.1
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-9.1

Then, create a pull request where the base branch is 9.1 and the compare/head branch is backport-5385-to-9.1.