WikiTemplateIT#createWikiFromTemplateTest is flickering

Symptom

org.xwiki.wiki.test.ui.WikiTemplateIT#createWikiFromTemplateTest sometimes fails because the wiki creation job fails to resolve the template extension, the Maven repository answering with a 503:

org.junit.ComparisonFailure: expected:<[Done!]> but was:<[Failed! HttpResponseException: status code: 503, reason phrase: Service Unavailable (503)

org.xwiki.extension.ResolveException: Failed to resolve artifact [maven:templateextension:jar:1.0] descriptor
 at org.xwiki.extension.repository.aether.internal.AetherExtensionRepository.resolveMaven(AetherExtensionRepository.java:580)
 ...
 at org.xwiki.extension.job.internal.AbstractInstallPlanJob.resolveExtension(AbstractInstallPlanJob.java:940)

Occurrence

• https://ci.xwiki.org/job/XWiki%20Environment%20Tests/job/xwiki-platform/job/stable-17.10.x/320/ - stable-17.10.x, commit 87df7079518, PostgreSQL latest / Tomcat 11-jdk25 / S3 / Chrome

It passed in the other environments of the same build, and in the previous builds.

Local reproduction

Run 3 times locally on commit 87df7079518 with the same configuration: 3/3 passed.

The failure is a transient 503 from the repository serving templateextension while the test runs, so the test depends on that repository being available.