Update testcontainers-java monorepo to v1.21.0 (#166)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

pom.xml

@@ -20,7 +20,7 @@
     <jenkins.version>${jenkins.baseline}.3</jenkins.version>
     <gitHubRepo>jenkinsci/${project.artifactId}-plugin</gitHubRepo>
     <!-- Test dependencies version -->
-    <testcontainer.version>1.20.6</testcontainer.version>
+    <testcontainer.version>1.21.0</testcontainer.version>
   </properties>
   <dependencyManagement>
     <dependencies>