Update non library packages to Java 21

[JohT]

🚀 Feature

• Migrate non-library packages to Java 21

[Copilot]

Pull request overview

This PR migrates the project’s non-library build/runtime configuration to Java 21, updating Maven and CI settings accordingly while modernizing test dependencies.

Changes:

• Bump the root Maven build java.version to 21 and upgrade Mockito usage (mockito-all → mockito-core, Mockito 5.5.0).
• Update the integration-test module POM to inherit from the parent (removing local Java 8 config and some duplicated plugin/test version properties).
• Update GitHub Actions workflows to run CI and CodeQL with Java 21 and remove the separate Java 8 setup for integration tests.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
pom.xml	Sets Java 21 at the parent level; upgrades Mockito; adjusts changelog plugin execution scope; adds surefire locale settings.
type-alias-axon-serializer/pom.xml	Replaces deprecated mockito-all with mockito-core for tests.
type-alias-axon-serializer-integration-test/pom.xml	Adds alias-parent as parent and removes module-local Java 8 property and some duplicated version properties.
.github/workflows/continuous-integration.yml	Switches CI Java version to 21 and removes the extra JDK 8 setup step.
.github/workflows/codeql-analysis.yml	Ensures CodeQL Java analysis uses a configured JDK 21.

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