Upgrade testcontainers 1.20.1 -> 1.21.4

Author: groldan

geowebcache/pom.xml

@@ -131,7 +131,7 @@
       <dependency>
         <groupId>org.testcontainers</groupId>
         <artifactId>testcontainers-bom</artifactId>
-        <version>1.20.1</version>
+        <version>1.21.4</version>
         <type>pom</type>
         <scope>import</scope>
       </dependency>