fix(buildkite): improve error handling for HTTP requests and add fallback for 404 responses

[MattDevy]

Elasticsearch version 9.1.0-SNAPSHOT doesn't exist in https://artifacts-api.elastic.co/v1/versions/9.1.0-SNAPSHOT in these cases we should fallback to version without -SNAPSHOT

Fixes buildkite test issue on main (and 9.1 branch)

See error:

INFO: Retrieving Elasticsearch Version & Hash from container...
--
  | INFO: Download Elasticsearch specs...
  | 2025/11/09 00:04:22 0 builds found
  | 2025/11/09 00:04:22 Build found :
  | 2025/11/09 00:04:22 Zipfile url :
  | 2025/11/09 00:04:22 Cannot download zip from , reason : Get "": unsupported protocol scheme ""

[prodsecmachine]

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[github-actions]

The backport to 8.19 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-8.19 8.19
# Navigate to the new working tree
cd .worktrees/backport-8.19
# Create a new branch
git switch --create backport-1040-to-8.19
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick --mainline 1 b5631f47c95408861ad6d0630953ed1b7c515fa9
# Push it to GitHub
git push --set-upstream origin backport-1040-to-8.19
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-8.19

Then, create a pull request where the base branch is 8.19 and the compare/head branch is backport-1040-to-8.19.