Disable housekeeping for design repos

What does this MR do and why?

Related issue: #415541 (closed)

This change makes sure housekeeping is not executed for design repos since it is not supported. Executing housekeeping was causing a NoMethodError that was blocking syncing on Geo.

Screenshots or screen recordings

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Before

DesignManagement::Repository.first.replicator.send(:sync_repository)

NoMethodError: undefined method `increment_pushes_since_gc' for #<DesignManagement::Repository id:1 >
from /Users/aakritigupta/.asdf/installs/ruby/3.1.4/lib/ruby/gems/3.1.0/gems/activemodel-6.1.7.2/lib/active_model/attribute_methods.rb:469:in `method_missing'

After

DesignManagement::Repository.first.replicator.send(:sync_repository)

nil

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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