[release-v2.6] Docs: fix trace:rootService example code #9593

Job	Run time
Lint	3m 5s
Run Unit Tests (test-with-cover-pkg)	3m 6s
Run Unit Tests (test-with-cover-tempodb)	16m 4s
Run Unit Tests (test-with-cover-tempodb-wal)	10m 44s
Run Unit Tests (test-with-cover-others)	11m 55s
Build	1m 44s
Run integration tests (test-e2e)	20m 14s
Run integration tests (test-integration-poller)	8m 55s
Benchmark	9m 29s
Run integration tests (test-e2e-deployments)	13m 9s
Run integration tests (test-e2e-serverless)	6m 41s
Check jsonnet & tempo-mixin	45s
Vendor check	1m 42s
Build technical documentation	23s
	1h 47m 56s

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