fix: Fix warning due to unchecked cast. (#241)

Author: dpcollins-google

google-cloud-pubsublite/src/main/java/com/google/cloud/pubsublite/ProjectBuilderHelper.java

@@ -20,12 +20,10 @@ abstract class ProjectBuilderHelper<Builder extends ProjectBuilderHelper<Builder
  public abstract Builder setProject(ProjectIdOrNumber project);
 
  public Builder setProject(ProjectId project) {
- setProject(ProjectIdOrNumber.of(project));
- return (Builder) this;
+ return setProject(ProjectIdOrNumber.of(project));
  }
 
  public Builder setProject(ProjectNumber project) {
- setProject(ProjectIdOrNumber.of(project));
- return (Builder) this;
+ return setProject(ProjectIdOrNumber.of(project));
  }
 }