ci: Do not run the autogenerated GAPICs unit tests

[lqiu96]

Part of #13296

[gemini-code-assist]

Code Review

This pull request introduces a configuration in the parent POM to exclude generated client unit tests directly under versioned packages from the Maven Surefire plugin to optimize CI execution time, while allowing specific modules like google-cloud-bigquerystorage to override this behavior. However, nesting the comma-separated property ${surefire.excludes} inside an tag prevents Maven from splitting the patterns correctly, making the exclusion ineffective. It is recommended to pass the property directly to the element instead.

[gemini-code-assist]

In Maven, when a plugin parameter is of type List (like excludes in maven-surefire-plugin), nesting a comma-separated property inside an <exclude> tag prevents Maven from splitting the string. It treats the entire comma-separated value as a single literal pattern containing a comma, which will fail to match any files and render the exclusion ineffective.

To allow Maven to correctly split the comma-separated property ${surefire.excludes} into individual list elements, pass the property directly to the <excludes> element.

          <excludes>${surefire.excludes}</excludes>