Add configuration for ArcMutate GitHub gradle plugin to delete old summaries when mutation testing is rerun against a GitHub PR. (#984)

Author: MartinWheelerMT

service/build.gradle

@@ -160,6 +160,10 @@ pitest {
 	threads = project.getGradle().getStartParameter().getMaxWorkerCount()
 }
 
+pitestGithub {
+	deleteOldSummaries = true
+}
+
 bootJar {
 	exclude("**/TransformJsonToXml*")
 }