ci: migrate Debian PHP images to Trixie

[matyhtf]

Summary

• Use official PHP Trixie base images for PHP 8.2–8.5, including ZTS variants.
• Replace removed PCRE1 development packages with libpcre2-dev and use the current FreeType development package name.
• Retire Debian PHP 8.1/8.1-zts builds; retain Alpine variants for compatibility testing.
• Publish explicit -trixie tags alongside existing tags.
• Build images on pull requests without publishing, and verify Debian Trixie, libcurl >= 8.0.0, and HTTP/2 support.

Motivation

Swoole's swoole_curl/multi/http2_duplex_stall.phpt exposes an HTTP/2 upload busy loop in Bookworm's libcurl 7.88.1. The upstream fix is available in newer libcurl releases. Trixie provides libcurl 8.14.1.

Affected CI: https://github.com/swoole/swoole-src/actions/runs/36699004423/job/109846262639

Validation

• PHP syntax checks for the generator and Debian template passed.
• Regenerating Dockerfiles is deterministic; all eight Debian matrix entries match their Trixie base tags.
• Debian package availability and generated workflow shell syntax checked.
• git diff --check passed.
• Full Docker builds will run in this PR workflow; the local Docker daemon requires unavailable sudo credentials.

Rollout

Merge this change and wait for the image publishing workflow to complete before updating swoole-src to consume the explicit -trixie tags.