CMS 5.2.0-beta1. Regression test: Calling `get_class()` without arguments is deprecated

[sabina-talipova]

Description

Test is failed because of Server Error Calling get_class() without arguments is deprecated. It's failed only in PHP 8.3 environment. Executed on: SC PHP 8.3 Firefox sink Test failed: https://studio.cucumber.io/projects/301855/test-runs/946350/folder-snapshots/11133993/scenario-snapshots/34725739/test-snapshots/46397535

Acceptance criteria

• All instances of get_class() being called without a parameter in the sink are updated to avoid deprecation warnings.
• Update the changelog which currently says no code changes were required to add PHP 8.3 support.

PRs

• https://github.com/silverstripe/silverstripe-versionfeed/pull/103
• https://github.com/silverstripe/silverstripe-documentconverter/pull/73
• https://github.com/silverstripe/developer-docs/pull/483

[maxime-rainville]

There's 4 instances that I could find