chore: update library-generation image to use latest alpine

[diegomarquezp]

This image has rsync 4.x, however other existing images may still have rsync 3.x

Next steps:

• [ ] merge this PR
• [ ] wait for next release of sdk-platform-java
• [ ] ensure all downstream repos use the latest image
• [ ] remove old versions of this image

[sonarqubecloud[bot]]

Quality Gate passed for 'gapic-generator-java-root'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[sonarqubecloud[bot]]

Quality Gate passed for 'java_showcase_integration_tests'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud