Update confluentinc/cp-zookeeper Docker tag to v7.6.1

This MR contains the following updates:

Package	Type	Update	Change
confluentinc/cp-zookeeper		minor	7.4.4-1-ubi8 -> 7.6.1-1-ubi8
confluentinc/cp-zookeeper	ironbank-docker	minor	7.4.4 -> 7.6.1
confluentinc/cp-zookeeper	stage	minor	7.4.4 -> 7.6.1

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