Bump github.com/stretchr/testify from 1.8.2 to 1.9.0 in /exporter/otlpexporter #764

Job	Run time
setup-environment	30s
test-coverage	1m 15s
lint	1m 31s
checks	29s
cross-build-collector (darwin, amd64)	17s
cross-build-collector (darwin, arm64)	16s
unittest (1.20)	1m 17s
cross-build-collector (linux, 386)	17s
unittest (1.19)	1m 17s
cross-build-collector (linux, amd64)	17s
cross-build-collector (linux, arm64)	18s
cross-build-collector (linux, ppc64le)	17s
cross-build-collector (linux, arm)	21s
cross-build-collector (windows, 386)	16s
cross-build-collector (windows, amd64)	15s
	8m 53s

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