That was the only difference for us as well. The CI/CD process built container images. Only difference between dev, test, and prod was the environment variables passed to the container.
At first I asked the clueless security analyst to explain how that improves security, which he couldn’t. Then I asked him how testing against one repository and deploying from another wouldn’t invalidate the results of the testing done by the QA team, but he kept insisting we needed it to check some box. I asked about the source of the policy and still no explanation, at least not one that made any sense.
Security analyst escalated it to his (thankfully not clueless) boss who promptly gave our process a pass and pointed out to Mr security analyst that literally nobody does that.