Update ghcr.io/backstage/backstage Docker tag to v1.33.6

This MR contains the following updates:

Package	Type	Update	Change
ghcr.io/backstage/backstage		patch	1.33.5 -> 1.33.6
ghcr.io/backstage/backstage	ironbank-docker	patch	1.33.5 -> 1.33.6
ghcr.io/backstage/backstage	stage	patch	1.33.5 -> 1.33.6

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