Use semconv pkg for schema URL in fetch.go

sdk/resource/internal/schema/generate/schema/fetch.go

@@ -20,20 +20,17 @@ import (
 	"log"
 	"net/http"
 	"os"
-)
-
-const (
-	// schemaURL is the target schema to download.
-	schemaURL = "https://opentelemetry.io/schemas/1.21.0"
 
-	// dest is the output file.
-	dest = "schema.yaml"
+	semconv "go.opentelemetry.io/otel/semconv/v1.21.0"
 )
 
+// dest is the output file.
+const dest = "schema.yaml"
+
 func run() error {
-	resp, err := http.Get(schemaURL)
+	resp, err := http.Get(semconv.SchemaURL)
 	if err != nil {
-		return fmt.Errorf("failed to download %q: %w", schemaURL, err)
+		return fmt.Errorf("failed to download %q: %w", semconv.SchemaURL, err)
 	}
 	defer resp.Body.Close()