spec: Do not stub temporary repo in sync service shared examples

When synchronizing repositories, then depending on a retry counter we
may either fetch into the real repository, or recreate the repo by first
creating a temporary staging repository, populating that repository and
then moving it into place. Our tests stub out this logic though such
that we always end up fetching into the real repository: this both keeps
us from exercising whether we fetch into the expected repo, and this
logic will break when Gitaly changes semantics of the CreateRepository
RPC to raise an error if the repository exists already.

Fix this issue by not stubbing out the temporary repository. Instead, we
now assert that function calls end up using the correct repository.

ee/spec/support/shared_examples/services/base_sync_service_shared_examples.rb

@@ -102,16 +102,15 @@ end
 
 RSpec.shared_examples 'sync retries use the snapshot RPC' do
   context 'snapshot synchronization method' do
-    before do
-      allow(subject).to receive(:temp_repo) { repository }
-    end
+    let(:temp_repo) { subject.send(:temp_repo) }
 
     def receive_create_from_snapshot
-      receive(:create_from_snapshot).with(primary.snapshot_url(repository), match(/^GL-Geo/)) { Gitaly::CreateRepositoryFromSnapshotResponse.new }
+      receive(:create_from_snapshot).with(primary.snapshot_url(temp_repo), match(/^GL-Geo/)) { Gitaly::CreateRepositoryFromSnapshotResponse.new }
     end
 
     it 'does not attempt to snapshot for initial sync' do
       expect(repository).not_to receive_create_from_snapshot
+      expect(temp_repo).not_to receive_create_from_snapshot
       expect(subject).to receive(:fetch_geo_mirror).with(repository)
 
       subject.execute
@@ -121,6 +120,7 @@ RSpec.shared_examples 'sync retries use the snapshot RPC' do
       registry_with_retry_count(retry_count - 1)
 
       expect(repository).not_to receive_create_from_snapshot
+      expect(temp_repo).not_to receive_create_from_snapshot
       expect(subject).to receive(:fetch_geo_mirror).with(repository)
 
       subject.execute
@@ -130,16 +130,18 @@ RSpec.shared_examples 'sync retries use the snapshot RPC' do
       let!(:registry) { registry_with_retry_count(retry_count + 1) }
 
       it 'attempts to snapshot' do
-        expect(repository).to receive_create_from_snapshot
-        expect(subject).not_to receive(:fetch_geo_mirror).with(repository)
+        expect(repository).not_to receive_create_from_snapshot
+        expect(temp_repo).to receive_create_from_snapshot
+        expect(subject).not_to receive(:fetch_geo_mirror).with(temp_repo)
         expect(subject).to receive(:set_temp_repository_as_main)
 
         subject.execute
       end
 
       it 'attempts to fetch if snapshotting raises an exception' do
-        expect(repository).to receive_create_from_snapshot.and_raise(ArgumentError)
-        expect(subject).to receive(:fetch_geo_mirror).with(repository)
+        expect(repository).not_to receive_create_from_snapshot
+        expect(temp_repo).to receive_create_from_snapshot.and_raise(ArgumentError)
+        expect(subject).to receive(:fetch_geo_mirror).with(temp_repo)
 
         subject.execute
       end