Update dependency org.testcontainers:testcontainers to v1.21.0

Author: renovate[bot]

docker-network-client/pom.xml

@@ -15,7 +15,7 @@
 
 	<properties>
 		<rest-assured.version>4.5.1</rest-assured.version>
-		<testcontainers.version>1.20.6</testcontainers.version>
+		<testcontainers.version>1.21.0</testcontainers.version>
 	</properties>
 
 	<dependencies>