fix(federation): reset retainJob at start of run()

[solracsf]

Summary

JobList::buildJob resolves the job class via Server::get(), and the SimpleContainer caches the resulting instance as a singleton. When the cron loop processes multiple GetSharedSecret or RequestSharedSecret rows in the same pass, the same PHP object is reused, so a prior failure's $this->retainJob = true persisted into the next row's success path. The overridden start() then re-queued an already-successful handshake, causing continuous secret rotation against healthy peers.

Reset $this->retainJob = false at the top of run() so each invocation starts from a known state regardless of prior state on the cached instance.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI