Upgrade to Gradle 9.2.1 and enable Java 21 build support

[dividedmind]

Upgrades the project to use Gradle 9.2.1, allowing the build to run on Java 21 environments while maintaining Java 8 bytecode compatibility.

Key changes:

• Upgrade Gradle Wrapper to 9.2.1.
• Update CI workflows to use Java 21.
• Set options.release = 8 to ensure Java 8 compatibility (replaces obsolete source/target compatibility).
• content: upgrade shadow plugin to 9.3.1 and nexus-publish to 2.0.0.
• Fix Gradle 9 deprecation warnings (property assignment syntax).
• Fix ShadowRelocation task compatibility with new Gradle API.
• Bump Gradle version to 8.5 in some test code incompatible with 9.

[Copilot]

Pull request overview

This pull request upgrades the project from Gradle 7.4.2 to 9.2.1, enabling builds on Java 21 while maintaining Java 8 bytecode compatibility for the generated artifacts.

Key changes:

• Gradle wrapper upgraded to 9.2.1 with updated wrapper scripts and properties
• Build toolchain updated to Java 21 in CI workflows
• Java compilation configured with options.release = 8 instead of deprecated sourceCompatibility/targetCompatibility
• Shadow plugin upgraded from 7.1.2 to 9.3.1 and nexus-publish plugin to 2.0.0
• Fixed Gradle 9 deprecations: property assignments, archive classifiers, JaCoCo report configuration
• Updated ShadowRelocation task to work with Gradle 9 API changes

Reviewed changes

Copilot reviewed 13 out of 15 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
gradle/wrapper/gradle-wrapper.properties	Upgrades Gradle distribution to 9.2.1 and adds security properties
gradlew, gradlew.bat	Updates wrapper scripts to Gradle 9.2.1 versions with improved error handling and SPDX license identifier
gradle/wrapper/gradle-wrapper.jar	Binary update for Gradle 9.2.1 wrapper
build.gradle	Updates nexus-publish plugin to 2.0.0 and adds compiler args to suppress options warnings
buildSrc/build.gradle	Upgrades shadow plugin to 9.3.1 and fixes property assignment syntax
buildSrc/src/main/groovy/com/appland/tasks/ShadowRelocation.groovy	Fixes API compatibility with Gradle 9's Property API
runtime/build.gradle	Removes deprecated jcenter repository and updates Java compatibility to use options.release = 8
annotation/build.gradle	Updates Java compatibility settings and fixes deprecated property assignments (classifier, groupId, artifactId)
agent/build.gradle	Updates shadow plugin usage, Java compatibility, adds JUnit platform launcher dependency, and modernizes property syntax
.github/workflows/build-and-test.yml	Updates CI to use Java 21 for builds and adds Java 21 to test matrix
.github/workflows/release.yml	Updates release workflow to use Java 21
agent/test/jdbc/gradle/wrapper/gradle-wrapper.properties	Uses Gradle 8.5 for test code incompatible with Gradle 9
agent/test/httpcore/httpcore.bats	Improves path handling and changes server port configuration

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