chore(genai): replace deprecated genai image generation model

[alarconesparza]

Description

Fixes internal
b/505834660
b/507049205

Checklist

• I have followed Sample Format Guide
• pom.xml parent set to latest shared-configuration
• Appropriate changes to README are included in PR
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• Tests pass: mvn clean verify required
• Lint passes: mvn -P lint checkstyle:check required
• Static Analysis: mvn -P lint clean compile pmd:cpd-check spotbugs:check advisory only
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

[gemini-code-assist]

Code Review

This pull request updates the virtual try-on model ID to 'virtual-try-on-001' in the sample code and integration tests. It also removes the test scope for the 'google-cloud-storage' dependency in the pom.xml. A review comment points out that this dependency should remain in the test scope to avoid unnecessary compile-time dependencies and a larger artifact footprint.