Fix unit tests to avoid data race in pipelines

[salonichf5]

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Proposed changes

Write a clear and concise description that helps reviewers understand the purpose and impact of your changes. Use the following format:

Problem: Users want to parallelize unit tests without having data race issues

Solution: Modify unit tests to be independent of variables, maps/structs to avoid data race when tests run in parallel.

Testing: Manual Testing

1. run make unit-test 10-12 times. Passes all the time
2. run tests 10-12 times in the folder https://github.com/nginxinc/nginx-gateway-fabric/tree/main/internal/mode/static/state/graph , where most of the data race failures were happening.

Please focus on (optional): If you any specific areas where you would like reviewers to focus their attention or provide specific feedback, add them here.

Closes #2569 Closes #2578

Checklist

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• [x] I have read the CONTRIBUTING doc
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have checked that all unit tests pass after adding my changes
• [ ] I have updated necessary documentation
• [x] I have rebased my branch onto main
• [x] I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

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