[0.25.x] Bump GRPC to 1.56.3

[khrm]

This addresses the CVE CVE-2023-44487.

Changes

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Release Notes

This addresses the CVE https://github.com/advisories/GHSA-qppj-fm5r-hxr3.

[khrm]

/kind security

[khrm]

@vdemeester @savitaashture Let's merge this. We need to do a release again with an updated GRPC.

[vdemeester]

/approve
/lgtm

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