pause: Update to version 3.7-master-21

Update container-registry.zalando.net/teapot/pause to version 3.7-master-21

Author: zalando-teapot-robot

cluster/manifests/e2e-resources/pool-reserve.yaml

@@ -46,7 +46,7 @@ spec:
       terminationGracePeriodSeconds: 0
       containers:
       - name: pause
-        image: container-registry.zalando.net/teapot/pause:3.4.1-master-18
+        image: container-registry.zalando.net/teapot/pause:3.7-master-21
         resources:
           limits:
             cpu: 1m