Update quay.io/skupper/skupper-router Docker tag to v2.6.0

This MR contains the following updates:

Package	Type	Update	Change
quay.io/skupper/skupper-router		minor	2.5.2 -> 2.6.0
quay.io/skupper/skupper-router	ironbank-docker	minor	2.5.2 -> 2.6.0
quay.io/skupper/skupper-router	stage	minor	2.5.2 -> 2.6.0

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