ci: tell sonar where the jacoco root report is (#2796)

The aggregated jacocoRootReport is not in one of the standard locations
searched by sonar, add a property with the report file path so sonar can
reflect the coverage

gradle/sonar.gradle

@@ -6,6 +6,7 @@ sonar {
         property 'sonar.organization', 'spotbugs'
         property 'sonar.projectKey', 'com.github.spotbugs.spotbugs'
         property 'sonar.projectName', 'SpotBugs'
+        property 'sonar.coverage.jacoco.xmlReportPaths', "${buildDir}/reports/jacoco/jacocoRootReport/jacocoRootReport.xml"
     }
 }