Bump go.opentelemetry.io/otel/sdk from 1.20.0 to 1.21.0 #847

Job	Run time
govulncheck	1m 15s
setup-environment	22s
lint	1m 26s
checks	28s
test-coverage	1m 20s
cross-build-collector (darwin, amd64)	13s
unittest-matrix (~1.21.4)	1m 24s
cross-build-collector (darwin, arm64)	7s
unittest-matrix (~1.20.11)	1m 24s
cross-build-collector (linux, 386)	13s
cross-build-collector (linux, amd64)	8s
cross-build-collector (linux, arm64)	8s
cross-build-collector (linux, ppc64le)	10s
cross-build-collector (linux, arm, 7)	7s
cross-build-collector (linux, s390x)	7s
cross-build-collector (windows, 386)	13s
cross-build-collector (windows, amd64)	8s
unittest	1s
	9m 14s

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