test: mark stringbytes-external-max flaky on AIX

[sxa]

Another one in the set of tests marked flaky on AIX under #60565 - this is also exhibiting intermittent failing behaviour and is causing issues for PRs such as #60962 (comment) (which was on v24 so I'll backport to there once this is in)

Verifying it's level of flakiness in https://ci.nodejs.org/job/node-stress-single-test/628/ (Seems in the same ballpark as the others)

Screenshot from https://ci.nodejs.org/job/node-test-commit-aix/60068/nodes=aix72-ppc64/testReport/addons/tringbytes-external-exceed-max/ :

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/70437/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.54%. Comparing base (40c57ed) to head (13e357e).
⚠️ Report is 11 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@ ## main #60995 +/- ## ========================================== + Coverage 88.53% 88.54% +0.01%  ========================================== Files 703 703 Lines 208432 208432 Branches 40195 40196 +1 ========================================== + Hits 184526 184555 +29  + Misses 15925 15890 -35  - Partials 7981 7987 +6 

see 42 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/70442/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/70452/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/70464/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/70466/

[nodejs-github-bot]

Landed in e28656a