Add CHANGELOG entry for 3.0.0-beta3

Adds a CHANGELOG entry covering the three fixes that have landed on 3.0.x since 3.0.0-beta2 and are currently unreleased:

• 3459820 — "Call to protected method t()", the ContextAwarePluginAssignmentTrait / StringTranslationTrait conflict, resolved with an explicit insteadof. Landed as f4e7615, credit lawxen.
• 3531242 — the missing : void return type on submitConfigurationForm(). Drupal 11.2 declared that return type on BlockBase, which made our untyped override a fatal at class load and stopped drush updatedb outright. Core reverted it in 11.3, so the fatal is specific to 11.2.x. Landed as 039cb78, credit Seth Hill.
• 3614068 — the orphaned image component configuration. Landed as a2ff2bf via !14 (merged).

It also records two things found while fixing 3614068 that users would otherwise have no way to learn about, since they are not the subject of any issue:

• layout_builder_kit.image_component had no schema definition at all on this branch, so the settings form was writing a config object with none.
• layout_builder_kit.settings was declared type: config_entity when it is simple config.

And the fact that the test suite had never actually run: both test files carried a plural Tests suffix, which PHPUnit's *Test.php discovery does not collect, so the suite silently executed nothing. The branch now runs 12 tests.

Version choice

I have used 3.0.0-beta3, continuing the existing beta track rather than promoting to stable, since nothing about these fixes constitutes a stability claim about the D10/D11 line. Say the word if you would rather cut this as 3.0.0 or 3.0.1 and I will amend.

Note

This branch has no GitLab CI, so no pipeline will run here — see #3614091. Documentation only; no code changes.