Added @internal annotation

Added annotation so that gradle does not complain.

See more here https://docs.gradle.org/7.4.2/userguide/validation_problems.html#missing_annotation

Author: hamsterready

buildSrc/src/main/groovy/com.google.api-ads.java-conventions.gradle

@@ -162,6 +162,7 @@ disableUnlessPublishing(tasks.sourcesJar)
 class ExampleRunnerTask extends JavaExec {
 
   // The base package for all examples.
+  @Internal
   private String basePackage = 'com.google.ads.googleads.examples.'
 
   // Hints for failed executions.