chore(deps): update gradle to v9

[renovate-bot]

This PR contains the following updates:

Package	Update	Change
gradle	major	8-jdk21 → 9-jdk21

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[dpebot]

/gcbrun

[gemini-code-assist]

Code Review

This pull request updates the Gradle version from 8 to 9 in the cloudbuild.yaml configuration for both the test and assemble steps. A critical issue was raised regarding this change, as upgrading to a major version like Gradle 9 is likely to break the build due to a lack of support from the Spring Boot Gradle Plugin and other project dependencies.

[gemini-code-assist]

This update to Gradle 9, a major version, is likely to break the build. The Spring Boot Gradle Plugin, which this project uses, does not yet support Gradle 9. For instance, the latest Spring Boot versions explicitly state that Gradle 9.x is not yet supported. Using an unsupported Gradle version can lead to build failures and unpredictable behavior. It is recommended to wait until your project's dependencies, particularly the Spring Boot plugin, officially support Gradle 9.