[chore][receiver/splunkenterprisereceiver] run make modernize (open-telemetry#43374)

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#### Description

Run the `make modernize` tool.

https://pkg.go.dev/golang.org/x/tools/gopls/internal/analysis/modernize

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Signed-off-by: Paulo Dias <[email protected]>

Author: paulojmdias

receiver/splunkenterprisereceiver/search_result.go

@@ -146,7 +146,7 @@ type kvEntry struct {
 
 type kvStatus struct {
 	Current   kvStoreCurrent `json:"current"`
-	KVService kvService      `json:"externalKVStore,omitempty"`
+	KVService kvService      `json:"externalKVStore,omitzero"`
 }
 
 type kvService struct {