refactor test example indent

Signed-off-by: moonyoungCHAE <xpf_fl@naver.com>

Author: moonyoungCHAE

spring-kafka-docs/src/main/antora/modules/ROOT/pages/testing.adoc

@@ -163,16 +163,16 @@ public final class EmbeddedKafkaHolder {
     public static EmbeddedKafkaBroker getEmbeddedKafka() {
         if (!started) {
             synchronized (this) {
-		if (!started) {
-		    try {
-	                embeddedKafka.afterPropertiesSet();
-		    }
-	            catch (Exception e) {
-	                throw new KafkaException("Embedded broker failed to start", e);
-		    }
-	            started = true;
-		}
-	    }
+			if (!started) {
+		    		try {
+	        			embeddedKafka.afterPropertiesSet();
+		    		}
+	        		catch (Exception e) {
+	        			throw new KafkaException("Embedded broker failed to start", e);
+		    		}
+	        		started = true;
+				}
+			}
         }
         return embeddedKafka;
     }