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

• FIX Don't use deprecated usage of get_class() #103
• FIX Don't use deprecated usage of get_class() silverstripe-documentconverter#73
• DOC Minor change to changelog regarding PHP 8.3 developer-docs#483

[maxime-rainville]

There's 4 instances that I could find