CustomTypeTest.testTestCase1 fails due to whitespace; corrected

The issue was that the test emitted 3 spaces where the expectation file had 4.

https://jenkins.ci.cloudbees.com/job/plugins/job/xunit-plugin/org.jenkins-ci.plugins$xunit/lastCompletedBuild/testReport/org.jenkinsci.plugins.xunit.types/CustomTypeTest/testTestCase1/

in general, the test failure message wasn't helpful and should be revisited.