Update gcr.io/projectsigstore/rekor-server Docker tag to v1.3.6

This MR contains the following updates:

Package	Type	Update	Change
gcr.io/projectsigstore/rekor-server		patch	v1.3.5 -> v1.3.6
gcr.io/projectsigstore/rekor-server	ironbank-docker	patch	v1.3.5 -> v1.3.6
gcr.io/projectsigstore/rekor-server	stage	patch	v1.3.5 -> v1.3.6

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