[sdk-platform-java] Integration test, `test_generate_repo`, failed because difference found in `README.md` after releasing a new version of google-cloud-java

The integration test is to make sure no difference between certain libraries generated by `generated_repo.py` and google-cloud-java (at a specific committish).

We use a test branch of google-cloud-java, `test-hermetic-build`, to compare files so that files are locked. However, when generating `README.md`, the version of the library will be the latest version found in Maven central, thus we need to manually change the version in `README.md` in the test branch after a release of google-cloud-java.

The version is listed in following sections:

```

com.google.cloud
google-cloud-alloydb
0.26.0

implementation 'com.google.cloud:google-cloud-alloydb:0.26.0'

libraryDependencies += "com.google.cloud" % "google-cloud-alloydb" % "0.26.0"

[maven-version-link]: https://central.sonatype.com/artifact/com.google.cloud/google-cloud-alloydb/0.26.0
```

We shouldn't need to manually modify the version after releasing google-cloud-java to maintain integration tests.