Revert "Disable running tests on Jenkins"

With the extra memory in the parent commit the build is succeeding again
and therefore we don't need tests disabled anymore.

This reverts commit bee7e0d.

Jenkinsfile

@@ -38,7 +38,6 @@ 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 \