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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• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• 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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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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

Additional details and impacted files

@@           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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