[Java] Run Mockito as Agent, i.e. fix the following warning.

BufferUtilTest > freeIsANoOpIfDirectBufferContainsNonDirectByteBuffer() STANDARD_ERROR
    Mockito is currently self-attaching to enable the inline-mock-maker. This will no longer work in future releases of the JDK. Please add Mockito as an agent to your build what is described in Mockito's documentation: https://javadoc.io/doc/org.mockito/mockito-core/latest/org/mockito/Mockito.html#0.3

build.gradle

@@ -268,6 +268,15 @@ project(':agrona') {
         testRuntimeOnly 'org.junit.platform:junit-platform-launcher'
     }
 
+    def mockitoAgent = configurations.create('mockitoAgent') { transitive = false }
+    mockitoAgent.withDependencies {it.add(libs.mockito.get()) }
+
+    tasks {
+        test {
+            jvmArgs("-javaagent:${mockitoAgent.asPath}")
+        }
+    }
+
     def generatedDir = file("${layout.buildDirectory.get()}/generated-src")
     sourceSets {
         generated {