Change download.apache.org to https://dlcdn.apache.org

That should unstuck the current failing build [1].

• [1] https://jenkins.softwareheritage.org/job/jenkins-tools/job/swh-jenkins-dockerfiles/1136/console

Related to swh/infra/sysadm-environment#4615 (closed)

Test Plan

• local build ok
• curl query from thyssen where it used to block with the previous mirror ok (see task comment)

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Migrated from D8642 (view on Phabricator)