Bump github.com/stretchr/testify from 1.8.4 to 1.9.0 in /pkg/experimentalmetricmetadata #15020

Job	Run time
govulncheck (receiver-0)	2m 19s
setup-environment	0s
govulncheck (receiver-1)	1m 39s
govulncheck (processor)	2m 53s
govulncheck (exporter)	3m 21s
govulncheck (extension)	1m 59s
govulncheck (connector)	2m 13s
govulncheck (internal)	3m 15s
govulncheck (pkg)	2m 46s
build-examples	0s
check-codeowners	0s
check-collector-module-version	0s
checks	0s
correctness-metrics	0s
correctness-traces	0s
integration-tests	0s
lint-matrix	0s
unittest-matrix	0s
lint	0s
unittest	0s
coverage	0s
cross-compile	0s
build-package	0s
windows-msi	0s
publish-check	0s
publish-dev	0s
publish-stable	0s
rotate-milestone	0s
	20m 25s

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