Fix synonyms/put_synonym_rule body

[pquentin]

synonyms is not a list, but a string in Solr format.

[github-actions]

Following you can find the validation results for the API you have changed.

API	Status	Request	Response
synonyms.put_synonym_rule	🔴	4/4	3/4

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

[carlosdelest]

Thanks for fixing this!

[github-actions]

The backport to 8.11 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-8.11 8.11
# Navigate to the new working tree
cd .worktrees/backport-8.11
# Create a new branch
git switch --create backport-2407-to-8.11
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 90b09673b22aa4537a2339470dc123d03f167f3b
# Push it to GitHub
git push --set-upstream origin backport-2407-to-8.11
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-8.11

Then, create a pull request where the base branch is 8.11 and the compare/head branch is backport-2407-to-8.11.

[pquentin]

The backport to 8.11 failed:

Opened #2409, the conflict was output/openapi/elasticsearch-serverless-openapi.json which isn't in 8.11.