[chore] [exporter/splunkhec] discard response body (#33587) #24

Job	Run time
windows-unittest-matrix (receiver-0)	18m 41s
windows-unittest-matrix (receiver-1)	20m 59s
windows-unittest-matrix (receiver-2)	21m 31s
windows-unittest-matrix (receiver-3)	17m 10s
windows-unittest-matrix (processor-0)	10m 49s
windows-unittest-matrix (processor-1)	16m 21s
windows-unittest-matrix (exporter-0)	15m 15s
windows-unittest-matrix (exporter-1)	20m 57s
windows-unittest-matrix (exporter-2)	21m 37s
windows-unittest-matrix (exporter-3)	14m 46s
windows-unittest-matrix (extension)	15m 12s
windows-unittest-matrix (connector)	14m 47s
windows-unittest-matrix (internal)	18m 42s
windows-unittest-matrix (pkg)	12m 51s
windows-unittest-matrix (cmd-0)	8m 39s
windows-unittest-matrix (cmd-1)	16m 10s
windows-unittest-matrix (other)	29m 33s
windows-unittest	3s
	4h 54m 3s

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