AVIF support on Bookworm

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Fix: AVIF support for PHP 8.1/8.2 Bookworm images

Removed --with-external-gd from PHP 8.1 and 8.2 Dockerfiles. This ensures AVIF support is enabled by allowing PHP to build its bundled GD library, as Debian Bookworm's system libgd3 lacks AVIF compilation.

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