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

[JoeWang1127]

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:

<dependency>
  <groupId>com.google.cloud</groupId>
  <artifactId>google-cloud-alloydb</artifactId>
  <version>0.26.0</version>
</dependency>

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.