Update rook/ceph Docker tag to v1.13.6

This MR contains the following updates:

Package	Type	Update	Change
rook/ceph		patch	v1.13.5 -> v1.13.6
rook/ceph	ironbank-docker	patch	v1.13.5 -> v1.13.6
rook/ceph	stage	patch	v1.13.5 -> v1.13.6

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