#37 detect java+checkstyle warnings in CI

This fixes java and checkstyle warnings not being detected properly.

ci/Jenkinsfile

@@ -47,7 +47,7 @@ pipeline {
           }
 
           dir('java') {
-            mvn goal: 'clean verify -P sign', dependencies: 'dependencies/maven.deps'
+            mvn goal: 'clean verify checkstyle:checkstyle -P sign', dependencies: 'dependencies/maven.deps'
           }
         }
       }
@@ -76,7 +76,7 @@ pipeline {
         anyOf {
           buildingTag()
           branch 'main'
-          branch pattern: 'release/[0-9.]+', comparator: 'REGEXP'          
+          branch pattern: 'release/[0-9.]+', comparator: 'REGEXP'
           branch pattern: 'feature/\\w+', comparator: 'REGEXP'
         }
       }
@@ -94,6 +94,7 @@ pipeline {
       recordIssues aggregatingResults: true,
         enabledForFailure: true,
         tools: [
+          java(),
           checkStyle(),
           mavenConsole()],
         qualityGates: [[threshold: 1, type: 'TOTAL', unstable: true]]