Update confluentinc/cp-schema-registry Docker tag to v8.1.0

This MR contains the following updates:

Package	Type	Update	Change
confluentinc/cp-schema-registry	ironbank-docker	minor	8.0.2 -> 8.1.0
confluentinc/cp-schema-registry	stage	minor	8.0.2 -> 8.1.0

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