Use explicit foreign key names for Ci::Build

What does this MR do and why?

This change is needed for the Rails 7 upgrade: !90907 (merged)

Rails 6 uses active_record.name.foreign_key to compute the foreign key name:

        def derive_foreign_key
          if belongs_to?
            "#{name}_id"
          elsif options[:as]
            "#{options[:as]}_id"
          else
            active_record.name.foreign_key
          end
        end

but in Rails 7 it was changed to: active_record.model_name.to_s.foreign_key

        def derive_foreign_key
          if belongs_to?
            "#{name}_id"
          elsif options[:as]
            "#{options[:as]}_id"
          else
            active_record.model_name.to_s.foreign_key
          end
        end

For ci_builds we're changing model_name to Job and all foreign keys will be job_id unless explicitly set.

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