Update gcr.io/kasten-images/upgrade Docker tag to v8.0.12

This MR contains the following updates:

Package	Type	Update	Change
gcr.io/kasten-images/upgrade		patch	8.0.11 -> 8.0.12
gcr.io/kasten-images/upgrade	ironbank-docker	patch	8.0.11 -> 8.0.12
gcr.io/kasten-images/upgrade	stage	patch	8.0.11 -> 8.0.12

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