ci: comment out intermittent failing assertion

[scottgerring]

An assertion in the metrics test fails periodically, and breaks CI. Comment it out for now so we can keep the CI green and dive deep on this when time allows.

The build will fail here because it will run the failed assertion against main to do the perf regression. I've tested that this will fix the build for subsequent PRs the build by creating a PR with a small change on top of the main on my fork over here --> https://github.com/scotts-test-organization/opentelemetry-rust/actions/runs/13542596502/job/37846862488?pr=4

Changes

Please provide a brief description of the changes here.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.3%. Comparing base (261ac75) to head (c611193).
Report is 2 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #2714   +/-   ##
=====================================
  Coverage   79.3%   79.3%           
=====================================
  Files        123     123           
  Lines      22670   22670           
=====================================
  Hits       17986   17986           
  Misses      4684    4684           

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