grpc: do not use deprecated APIs in example code #2965

Job	Run time
Smoke Tests	0s
Prepare Go modules cache	57s
linux/amd64 golang:1.23-bookworm	1m 37s
macos-12 go1.23	6m 40s
linux/arm64 golang:1.23-bookworm	2m 55s
macos-latest (AppSec disabled)	1m 49s
linux/amd64 golang:1.23-bullseye	1m 33s
macos-12 go1.22	6m 15s
windows-latest (AppSec disabled)	2m 41s
linux/arm64 golang:1.23-bullseye	3m 3s
macos-14 go1.23	2m 39s
linux/amd64 golang:1.23-alpine	1m 16s
ubuntu-latest-16-cores (AppSec disabled)	1m 9s
linux/arm64 golang:1.23-alpine	2m 54s
macos-14 go1.22	2m 51s
linux/amd64 golang:1.22-bookworm	1m 27s
linux/arm64 golang:1.22-bookworm	2m 48s
linux/amd64 golang:1.22-bullseye	1m 18s
linux/arm64 golang:1.22-bullseye	2m 42s
linux/amd64 golang:1.22-alpine	1m 24s
linux/arm64 golang:1.22-alpine	2m 45s
	50m 43s

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