TestManifestAPI_Get_Schema1 returs 400 instead of 404

https://gitlab.com/gitlab-org/container-registry/-/jobs/11679933974

FAIL [MASKED]/handlers (coverage: 71.3% of statements)
=== Failed
=== FAIL: [MASKED]/handlers TestManifestAPI_Get_Schema1/by_tag (0.01s)
    api_integration_test.go:1162: 
        	Error Trace:	/builds/gitlab-org/container-[MASKED]/[MASKED]/handlers/api_integration_test.go:1162
        	Error:      	Not equal: 
        	            	expected: 400
        	            	actual  : 404
        	Test:       	TestManifestAPI_Get_Schema1/by_tag
    --- FAIL: TestManifestAPI_Get_Schema1/by_tag (0.01s)