Disable running tests on Jenkins

The Jenkins CI at EF is running very slowly recently and all
tests are timing out. The tests work fine locally and find
on GitHub actions runners.

Therefore on the Jenkins CI build without running the tests.

Jenkinsfile

@@ -38,6 +38,7 @@ pipeline {
               withCredentials([string(credentialsId: 'gpg-passphrase', variable: 'KEYRING_PASSPHRASE')]) {
                 sh '''/jipp/tools/apache-maven/latest/bin/mvn \
                       clean verify -B -V \
+                      -DskipTests=true \
                       -Dgpg.passphrase="${KEYRING_PASSPHRASE}"  \
                       -Dmaven.test.failure.ignore=true \
                       -DexcludedGroups=flakyTest,slowTest \