fix(tracing/propagation): set parent span correctly

[samugi]

Summary

Fix an issue where the parent span was set incorrectly when the balancer instrumentation was disabled (the parent span ID was set to a temporary balancer span that was never reported).

Checklist

• The Pull Request has tests
• There's an entry in the CHANGELOG
• (no) There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Full changelog

• [Implement ...]

Issue reference

https://konghq.atlassian.net/browse/KAG-2281
closes #11294

[team-gateway-bot]

The backport to release/3.3.x 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-release/3.3.x release/3.3.x
# Navigate to the new working tree
cd .worktrees/backport-release/3.3.x
# Create a new branch
git switch --create backport-11468-to-release/3.3.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 a6659edb925ba07306eb2be212df06dbcc5f2a9f
# Push it to GitHub
git push --set-upstream origin backport-11468-to-release/3.3.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release/3.3.x

Then, create a pull request where the base branch is release/3.3.x and the compare/head branch is backport-11468-to-release/3.3.x.