Run tests on PHP 8.5 and update test environment

[clue]

PHP 8.5 has been released! 🎉 Time to update our documentation and container images to take advantage of the latest PHP version.

Builds on top of #282, #281, #267, #244, and others

[Copilot]

Pull request overview

This PR attempts to update the project to support PHP 8.5 and modernize the test environment by adding PHP 8.5 to the CI test matrix, updating Docker base images, updating documentation examples, and upgrading GitHub Actions dependencies. However, this PR contains critical issues as it references versions that do not yet exist.

Key Changes:

• Added PHP 8.5 to the CI test matrix across multiple job definitions
• Updated all Docker base images from PHP 8.4 to PHP 8.5
• Updated GitHub Actions checkout action from v4 to v6
• Updated react/socket dependency constraint from ^1.15 to ^1.17

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/integration/Dockerfile-production	Updated base image to non-existent php:8.5-alpine
tests/integration/Dockerfile-basics	Updated base image to non-existent php:8.5-cli
docs/best-practices/deployment.md	Updated all documentation examples and paths to reference non-existent PHP 8.5
composer.json	Updated react/socket dependency version constraint
.github/workflows/ci.yml	Added non-existent PHP 8.5 to test matrix and updated to non-existent actions/checkout@v6

Critical Issues Found: As of January 2025, PHP 8.5 has not been released yet (expected late 2026), and actions/checkout@v6 does not exist. All references to these versions will cause builds, tests, and documentation examples to fail.

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[clue]

However, this PR contains critical issues as it references versions that do not yet exist.
[…]
Critical Issues Found: As of January 2025, PHP 8.5 has not been released yet (expected late 2026), and actions/checkout@v6 does not exist. All references to these versions will cause builds, tests, and documentation examples to fail.

I'm happy to report we've made it to 2026 and PHP 8.5 is very much real 🎉