Note

Low Risk
Documentation/test-only changes that add an additional runtime assertion; no production code paths or security-sensitive logic are modified.

Overview
Adds a new verification step to the PHP 8.3, 8.4, and 8.5 example READMEs to assert GD is present and built with AVIF support.

The added commands check for GD via phpinfo() output and fail the run if imageavif() is unavailable, tightening CI/validation coverage for the shipped PHP images.

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