Update titles and add toc

[linawolf]

Releases: main, 13.4, 12.4

[github-actions]

The backport to 12.4 failed:

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

stderr

error: could not apply 4ff2becf... Update titles and add toc
hint: After resolving the conflicts, mark them with
hint: "git add/rm <pathspec>", then run
hint: "git cherry-pick --continue".
hint: You can instead skip this commit with "git cherry-pick --skip".
hint: To abort and get back to the state before "git cherry-pick",
hint: run "git cherry-pick --abort".
hint: Disable this message with "git config set advice.mergeConflict false"

stdout

Auto-merging Documentation/Syntax/Operators/Index.rst
CONFLICT (content): Merge conflict in Documentation/Syntax/Operators/Index.rst

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-12.4 12.4
# Navigate to the new working tree
cd .worktrees/backport-12.4
# Create a new branch
git switch --create backport-1577-to-12.4
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick 4ff2becf705ab02ef98a7708ff85acd9f8f1f75d
# Push it to GitHub
git push --set-upstream origin backport-1577-to-12.4
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-12.4

Then, create a pull request where the base branch is 12.4 and the compare/head branch is backport-1577-to-12.4.