Update confluentinc/cp-kafka-rest Docker tag to v7.6.1

This MR contains the following updates:

Package	Type	Update	Change
confluentinc/cp-kafka-rest	ironbank-docker	minor	7.5.3 -> 7.6.1
confluentinc/cp-kafka-rest	stage	minor	7.5.3 -> 7.6.1

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