Update kafka to 1.21.3

Author: aiven-scala-steward[bot]

build.sbt

@@ -28,7 +28,7 @@ val scalaTestScalaCheckVersion  = s"$scalaTestVersion.0"
 val pekkoStreamCirceVersion     = "1.0.0"
 val diffxVersion                = "0.9.0"
 val testContainersVersion       = "0.40.16"
-val testContainersJavaVersion   = "1.19.8"
+val testContainersJavaVersion   = "1.21.3"
 val scalaCheckVersion           = "1.18.0"
 val scalaCheckOpsVersion        = "2.10.0"
 val enumeratumVersion           = "1.7.2"