Improve exception message when not a secondary

ee/lib/gitlab/geo/git_push_ssh_proxy.rb

@@ -93,7 +93,7 @@ module Gitlab
       end
 
       def ensure_secondary!
-        raise MustBeASecondaryNode, 'Node is not a secondary' unless Gitlab::Geo.secondary_with_primary?
+        raise MustBeASecondaryNode, 'Node is not a secondary or there is no primary Geo node' unless Gitlab::Geo.secondary_with_primary?
       end
     end
   end

ee/spec/lib/gitlab/geo/git_push_ssh_proxy_spec.rb

@@ -49,7 +49,7 @@ describe Gitlab::Geo::GitPushSSHProxy, :geo do
       it 'raises an exception' do
         expect do
           subject.info_refs
-        end.to raise_error(described_class::MustBeASecondaryNode)
+        end.to raise_error(described_class::MustBeASecondaryNode, 'Node is not a secondary or there is no primary Geo node')
       end
     end