test: relax test-memory-usage arrayBuffers check

[inoway46]

The previous GC-before-baseline approach did not make the exact arrayBuffers delta stable in CI.
Refs: #63214 (comment)

process.memoryUsage().arrayBuffers is process-wide, so unrelated ArrayBuffer/Buffer backing stores may be freed between snapshots. This keeps the test checking that the live 10 MiB ArrayBuffer is included, without requiring an exact process-wide delta.

Fixes: #63210

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.03%. Comparing base (facd71e) to head (4d4a78c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #63220      +/-   ##
==========================================
- Coverage   90.04%   90.03%   -0.01%     
==========================================
  Files         713      713              
  Lines      224950   224950              
  Branches    42530    42530              
==========================================
- Hits       202548   202536      -12     
+ Misses      14188    14183       -5     
- Partials     8214     8231      +17     

see 27 files with indirect coverage changes

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[aduh95]

CI: https://ci.nodejs.org/job/node-test-pull-request/73315/

[inoway46]

Could someone rerun the failed macOS jobs? The failures look unrelated to this PR.
https://github.com/nodejs/node/actions/runs/25622148862/job/75210643491?pr=63220