Lower upstream count for scale nfr test with nginx plus

[bjee19]

Problem: We were running into infrequent test failures due to nginx plus running out of memory when scaling upstreams.

Solution: Lower the upstream count when running with nginx plus by 2% of the previous maximum. Also, ran into an issue where the test had an incorrect WithTimeout check which caused an assertion to incorrectly only run once. Will monitor future NFR runs to see if this issue persists.

Testing: Ran the nfr scale test and it passed.

Closes #2563

Checklist

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• [x] I have read the CONTRIBUTING doc
• [ ] 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
• [x] I have updated necessary documentation
• [x] I have rebased my branch onto main
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Release notes

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 88.97%. Comparing base (0a4f0fb) to head (1a13b42). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2695 +/- ## ======================================= Coverage 88.97% 88.97% ======================================= Files 110 110 Lines 8615 8615 Branches 50 50 ======================================= Hits 7665 7665 Misses 892 892 Partials 58 58 ```

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