[chore] Fix CONTRIBUTING.md directions for adding a code owner (#29512) #576

Job	Run time
windows-unittest-matrix (receiver-0)	23m 13s
windows-unittest-matrix (receiver-1)	24m 29s
windows-unittest-matrix (processor)	16m 40s
windows-unittest-matrix (exporter)	23m 25s
windows-unittest-matrix (extension)	12m 1s
windows-unittest-matrix (internal)	14m 23s
windows-unittest-matrix (pkg)	11m 51s
windows-unittest-matrix (cmd)	26m 37s
windows-unittest-matrix (other)	23m 21s
windows-unittest	2s
	2h 56m 2s

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