Change BigQuery trace insert failure from error to warn log level #4978

Job	Run time
build-and-check	2m 24s
test-integration-packages/agent-runtime	45s
test-integration-backend	47s
test-integration-common	46s
test-integration-sdk	56s
test-integration-npm-app	52s
test-integration-cli	45s
test-integration-packages/internal	58s
test-integration-web	46s
test-integration-.agents	1m 14s
test-integration-packages/billing	47s
test-backend	41s
test-cli	1m 15s
test-packages/agent-runtime	1m 2s
test-common	42s
test-packages/internal	50s
test-.agents	50s
test-sdk	54s
test-web	49s
test-packages/billing	57s
test-npm-app	54s
	19m 54s

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