Support PHP 8.5 in GitHub Actions

Before opening a feature request against this repo, consider whether the feature should/could be implemented in the other OpenTelemetry client libraries. If so, please open an issue in opentelemetry-specification first.

Is your feature request related to a problem?

PHP 8.5 was released on November 20, 2025.
Currently, the GitHub Actions workflows in the following repositories do not include PHP 8.5 in their test matrices or Docker image build pipelines:

• open-telemetry/opentelemetry-php
• open-telemetry/opentelemetry-php-contrib

Describe the solution you'd like

Add PHP 8.5 support to the GitHub Actions workflows, including both CI testing and Docker image builds.
Based on a preliminary review, the following files may need to be updated (please let me know if I missed any):

• open-telemetry/opentelemetry-php
  • .github/workflows/publish-otel-php-base-docker-image.yml
• open-telemetry/opentelemetry-php-contrib
  • .github/workflows/php.yml

Describe alternatives you've considered

No

Additional context

No

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Start by inspecting .github/workflows/publish-otel-php-base-docker-image.yml in opentelemetry-php and .github/workflows/php.yml in opentelemetry-php-contrib. Compare their existing PHP version matrices and Docker build inputs, then update the workflows so PHP 8.5 is covered by CI testing and image builds. Done means both repositories' relevant GitHub Actions workflows pass with PHP 8.5 included.