Update fips-containers.istio.tetratelabs.com/proxyv2 Docker tag to v1.20.8

This MR contains the following updates:

Package	Type	Update	Change
fips-containers.istio.tetratelabs.com/proxyv2		patch	1.20.7 -> 1.20.8
fips-containers.istio.tetratelabs.com/proxyv2	ironbank-docker	patch	1.20.7-tetratefips-v0-distroless -> 1.20.8-tetratefips-v0-distroless
fips-containers.istio.tetratelabs.com/proxyv2	stage	patch	1.20.7-tetratefips-v0-distroless -> 1.20.8-tetratefips-v0-distroless

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