Update dependency istio/istio to v1.15.3

This MR contains the following updates:

Package	Type	Update	Change
istio/istio	ironbank-github	patch	1.15.2 -> 1.15.3
istio/istio		patch	1.15.2 -> 1.15.3

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Release Notes

istio/istio

v1.15.3

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