Follow-up from "testing/php81: security upgrade to 8.1.0 - CVE-2021-21707"

The following discussion from !27717 (merged) should be addressed:

@andypost started a discussion: (+2 comments)

Somehow on ppc64le builder it has 2 failed tests

FAILED TEST SUMMARY
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Silence operator does not leak out of fiber [Zend/tests/fibers/silence-operator-inside-fiber.phpt]
Silence operator does not leak into fiber [Zend/tests/fibers/silence-operator-outside-fiber.phpt]

Not clear why it passed on CI but fails on builder (and only this 2 tests for fibers)

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