Stop processing split queries on first error.

[jeschkies]

What this PR does / why we need it:
The TestMetricsTripperware became flaky after #10688. The race condition in the splitter has been there before but the change exposed it. When an error occurs, e.g. when query would be too large, the splitter would return. However, there was a small time window when the loop could still be fed a new request. #10688 just amplified this effect because it removed the serialization of requests and responses.

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• CHANGELOG.md updated
  • If the change is worth mentioning in the release notes, add add-to-release-notes label
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• For Helm chart changes bump the Helm chart version in production/helm/loki/Chart.yaml and update production/helm/loki/CHANGELOG.md and production/helm/loki/README.md. Example PR
• If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory.

[kavirajk]

Nice 👍

[dannykopping]

Was super pairing up with you to find and fix this 💪 great work!

[grafanabot]

Hello @jeschkies!
Backport pull requests need to be either:

• Pull requests which address bugs,
• Urgent fixes which need product approval, in order to get merged,
• Docs changes.

Please, if the current pull request addresses a bug fix, label it with the type/bug label.
If it already has the product approval, please add the product-approved label. For docs changes, please add the type/docs label.
If the pull request modifies CI behaviour, please add the type/ci label.
If none of the above applies, please consider removing the backport label and target the next major/minor release.
Thanks!

[grafanabot]

The backport to k173 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 branch
git switch --create backport-11067-to-k173 origin/k173
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x edae9d32eaf170d88628efc6374d546ce5c68cd4

When the conflicts are resolved, stage and commit the changes:

git add . && git cherry-pick --continue

If you have the GitHub CLI installed:

# Push the branch to GitHub:
git push --set-upstream origin backport-11067-to-k173
# Create the PR body template
PR_BODY=$(gh pr view 11067 --json body --template 'Backport edae9d32eaf170d88628efc6374d546ce5c68cd4 from #11067{{ "\n\n---\n\n" }}{{ index . "body" }}')
# Create the PR on GitHub
echo "${PR_BODY}" | gh pr create --title "[k173] Stop processing split queries on first error." --body-file - --label "size/S" --label "type/bug" --label "backport" --base k173 --milestone k173 --web

Or, if you don't have the GitHub CLI installed (we recommend you install it!):

# Push the branch to GitHub:
git push --set-upstream origin backport-11067-to-k173

# Create a pull request where the `base` branch is `k173` and the `compare`/`head` branch is `backport-11067-to-k173`.

# Remove the local backport branch
git switch main
git branch -D backport-11067-to-k173