Fixes #26199 - Fix dependency cycle when using git_repo

Previously this resulted in a dependency cycle. The tests didn't compile
so didn't catch it.

dependency cycles found: (File[/opt/puppetlabs/puppet/cache] => Class[Puppet::Server::Install] => Class[Puppet::Server::Config] => File[/opt/puppetlabs/puppet] => File[/opt/puppetlabs/puppet/cache])

a61e010e8d24f2e44ab1ebba0cc4382b05ce9d37 introduced this by managing
$sharedir in puppet::server::config. $vardir was managed in
puppet::server::install. Since sharedir is actually
/opt/puppetlabs/puppet and vardir is the cache directory within that, it
created a cycle.