Upgrade from Java 11 to Java 17

[devin-ai-integration]

Upgrade from Java 11 to Java 17

Summary

This PR upgrades the Spring Boot RealWorld application from Java 11 to Java 17. The changes update the Java version across the build configuration, CI pipeline, and documentation:

• build.gradle: Updated sourceCompatibility and targetCompatibility from '11' to '17'
• .github/workflows/gradle.yml: Updated JDK setup from version 11 to 17, and upgraded actions/cache from v2 to v3 (required to fix deprecation warning)
• README.md: Updated the "Getting started" section to reflect Java 17 requirement

All 68 tests pass successfully both locally and in CI with Java 17. Spring Boot 2.6.3 (used in this project) has official support for Java 17, and all current dependencies are compatible.

Review & Testing Checklist for Human

• Run the application locally with Java 17 and verify it starts without errors: ./gradlew bootRun
• Test core functionality by hitting a few key endpoints (e.g., curl http://localhost:8080/tags) to ensure no runtime issues

Notes

• The actions/cache version upgrade from v2 to v3 was necessary to fix a GitHub Actions deprecation error that was blocking CI
• No code logic changes were made - this is purely a Java version upgrade
• Link to Devin run: https://app.devin.ai/sessions/7986539420ae4007a40c2ac3799cabfd
• Requested by: Shawn Azman (shawn@cognition.ai) / @ShawnAzman

[devin-ai-integration]

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