Update quay.io/argoproj/argocd Docker tag to v2.1.8

This MR contains the following updates:

Package	Type	Update	Change
quay.io/argoproj/argocd	ironbank-docker	patch	v2.1.7 -> v2.1.8
quay.io/argoproj/argocd		patch	v2.1.7 -> v2.1.8
quay.io/argoproj/argocd	stage	patch	v2.1.7 -> v2.1.8

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