fix: add missing typing on TracerProvider.shutdown #756

Job	Run time
opentelemetry-api	37s
opentelemetry-exporter-opencensus	36s
opentelemetry-exporter-otlp-combined	40s
opentelemetry-exporter-otlp-proto-common	34s
opentelemetry-exporter-otlp-proto-grpc	41s
opentelemetry-exporter-otlp-proto-http	39s
opentelemetry-exporter-prometheus	33s
opentelemetry-exporter-zipkin-combined	38s
opentelemetry-exporter-zipkin-json	37s
opentelemetry-exporter-zipkin-proto-http	34s
opentelemetry-getting-started	53s
opentelemetry-opencensus-shim	37s
opentelemetry-opentracing-shim	37s
opentelemetry-propagator-b3	32s
opentelemetry-propagator-jaeger	33s
opentelemetry-proto-protobuf5	26s
opentelemetry-sdk	46s
opentelemetry-semantic-conventions	33s
opentelemetry-test-utils	32s
	11m 38s

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