Update istio/proxyv2 Docker tag to v1.20.5

This MR contains the following updates:

Package	Type	Update	Change
istio/proxyv2		patch	1.20.4 -> 1.20.5
istio/proxyv2	ironbank-docker	patch	1.20.4-distroless -> 1.20.5-distroless
istio/proxyv2	stage	patch	1.20.4-distroless -> 1.20.5-distroless

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