addons/stringbytes-external-exceed-max tests flake on AIX

[joyeecheung]

These are flaking in a strange way: they are supposed to be skipped due to not having enough memory, but the test hangs instead of exiting (presumably, since the printing already happened, process.exit() should have been called from common.skip())

For example: https://github.com/nodejs/reliability/blob/main/reports/2025-10-30.md

Reason	addons/stringbytes-external-exceed-max/test-stringbytes-external-exceed-max-by-1-utf8
Type	JS_TEST_FAILURE
Failed PR	5 (https://github.com/nodejs/node/pull/60434/, https://github.com/nodejs/node/pull/60388/, https://github.com/nodejs/node/pull/60387/, https://github.com/nodejs/node/pull/60380/, https://github.com/nodejs/node/pull/60427/)
Appeared	test-osuosl-aix72-ppc64_be-4
First CI	https://ci.nodejs.org/job/node-test-pull-request/69907/
Last CI	https://ci.nodejs.org/job/node-test-pull-request/69949/

Example

not ok 4623 addons/stringbytes-external-exceed-max/test-stringbytes-external-exceed-max-by-1-utf8
  ---
  duration_ms: 120069.84700
  severity: fail
  exitcode: -15
  stack: |-
    timeout
    1..0 # Skipped: intensive toString tests due to memory confinements
  ...

cc @nodejs/platform-aix