Fix panic when updating config concurrently

[bejjrajesh]

Proposed changes

This MR will fix the panic error happen when updating the nginx config concurrently.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• [x] I have read the CONTRIBUTING document
• [ ] I have run make install-tools and have attached any dependency changes to this pull request
• [ ] If applicable, I have added tests that prove my fix is effective or that my feature works
• [ ] If applicable, I have checked that any relevant tests pass after adding my changes
• [ ] If applicable, I have updated any relevant documentation (README.md)
• [ ] If applicable, I have tested my cross-platform changes on Ubuntu 22, Redhat 8, SUSE 15 and FreeBSD 13

[github-actions[bot]]

✅ All required contributors have signed the F5 CLA for this PR. Thank you!
_{Posted by the CLA Assistant Lite bot.}

[bejjrajesh]

I have hereby read the F5 CLA and agree to its terms

[dhurley]

@bejjrajesh Can you run the following make commands:

make install-tools
make deps

These will setup some tools, install git hooks and update the vendor folders.

[dhurley]

Closing this PR as further changes are required. This issue will be resolved by this new PR https://github.com/nginx/agent/pull/1088