skipper-canary-controller: Update to version main-21

Update container-registry.zalando.net/gwproxy/skipper-canary-controller to version main-21

Author: zalando-teapot-robot

cluster/manifests/skipper-canary-controller/canary-cronjob.yaml

@@ -26,7 +26,7 @@ spec:
           containers:
           - name: skipper-canary-controller
             terminationMessagePolicy: FallbackToLogsOnError
-            image: container-registry.zalando.net/gwproxy/skipper-canary-controller:main-20
+            image: container-registry.zalando.net/gwproxy/skipper-canary-controller:main-21
             env:
             - name: _PLATFORM_OBSERVABILITY_ACCESS_TOKEN
               valueFrom: