The Jenkins project builds Debian package which we import with reprepro. The documentation listed at https://wikitech.wikimedia.org/wiki/Jenkins#Get_the_package
The documentation there seems outdated since it still refers to jessie but we use stretch/buster. There is no mention of the component/ci component.
The Alternative upgrade method section bypasses reprepro. Apparently as a workaround to avoid updating unrelated packages.
I would like to revisit the process to import the Jenkins LTS package with a single way of clear instructions to import them (a runbook?). That would in turn lets anyone from SRE able to handle the operation, typically via the clinic duty.