fix(java-lang): Mark test as flaky (#10122)

Author: PerfectSlayer

dd-java-agent/instrumentation/java/java-lang/java-lang-21.0/src/test/groovy/VirtualThreadApiTest.groovy

@@ -1,8 +1,10 @@
 import datadog.trace.agent.test.InstrumentationSpecification
 import datadog.trace.api.Trace
 import datadog.trace.core.DDSpan
+import datadog.trace.test.util.Flaky
 
 // Note: test builder x2 + test factory can be refactored but are kept simple to ease with debugging.
+@Flaky("class loader deadlock on virtual thread clean up while Groovy do dynamic code generation - APMLP-782")
 class VirtualThreadApiTest extends InstrumentationSpecification {
   def "test Thread.Builder.OfVirtual - start()"() {
     setup: