Update cockroachdb/cockroach Docker tag to v20.2.7

This MR contains the following updates:

Package	Type	Update	Change
cockroachdb/cockroach	ironbank-docker	patch	v20.2.6 -> v20.2.7
cockroachdb/cockroach		patch	v20.2.6 -> v20.2.7
cockroachdb/cockroach	stage	patch	v20.2.6 -> v20.2.7

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