Validate that a WorkingDirectory task didn't contains any task with a workerGroup
### Feature description

Validate that a WorkingDirectory task didn't contains any task with a workerGroup as otherwise the workerGroup will be ignored leading to possible confusion.
core/src/main/java/io/kestra/core/validations/ValidationFactory.java
core/src/main/java/io/kestra/core/validations/ValidationFactory.java
core/src/test/java/io/kestra/core/validations/WorkingDirectoryTest.java
diff --git a/core/src/main/java/io/kestra/core/validations/ValidationFactory.java b/core/src/main/java/io/kestra/core/validations/ValidationFactory.java
index 724c9fc964..069a880240 100644
--- a/core/src/main/java/io/kestra/core/validations/ValidationFactory.java
+++ b/core/src/main/java/io/kestra/core/validations/ValidationFactory.java
@@ -176,6 +176,11 @@ ConstraintValidator<WorkingDirectoryTaskValidation, WorkingDirectory> workingDir
                 return false;
             }
 
+            if (value.getTasks().stream().anyMatch(task -> task.getWorkerGroup() != null)) {
+                context.messageTemplate("Cannot set a Worker Group in any WorkingDirectory sub-tasks, it is only supported at the WorkingDirectory level");
+                return false;
+            }
+
             return true;
         };
     }

diff --git a/core/src/test/java/io/kestra/core/validations/WorkingDirectoryTest.java b/core/src/test/java/io/kestra/core/validations/WorkingDirectoryTest.java
new file mode 100644
index 0000000000..82c54a430b
--- /dev/null
+++ b/core/src/test/java/io/kestra/core/validations/WorkingDirectoryTest.java
@@ -0,0 +1,88 @@
+package io.kestra.core.validations;
+
+import io.kestra.core.models.tasks.WorkerGroup;
+import io.kestra.core.models.validations.ModelValidator;
+import io.kestra.core.tasks.flows.Pause;
+import io.kestra.core.tasks.flows.WorkingDirectory;
+import io.kestra.core.tasks.log.Log;
+import io.micronaut.test.extensions.junit5.annotation.MicronautTest;
+import jakarta.inject.Inject;
+import org.junit.jupiter.api.Test;
+
+import java.time.Duration;
+import java.util.List;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.*;
+
+@MicronautTest
+public class WorkingDirectoryTest {
+    @Inject
+    private ModelValidator modelValidator;
+
+    @Test
+    void workingDirectoryValid()  {
+        var workingDirectory = WorkingDirectory.builder()
+            .id("workingDir")
+            .type(WorkingDirectory.class.getName())
+            .tasks(
+                List.of(Log.builder()
+                    .id("log")
+                    .type(Log.class.getName())
+                    .message("Hello World")
+                    .build()
+                )
+            )
+            .build();
+
+        assertThat(modelValidator.isValid(workingDirectory).isPresent(), is(false));
+    }
+
+    @Test
+    void workingDirectoryInvalid()  {
+        // empty list of tasks
+        var workingDirectory = WorkingDirectory.builder()
+            .id("workingDir")
+            .type(WorkingDirectory.class.getName())
+            .build();
+
+        assertThat(modelValidator.isValid(workingDirectory).isPresent(), is(true));
+        assertThat(modelValidator.isValid(workingDirectory).get().getMessage(), containsString("The tasks property cannot be empty"));
+
+        // flowable task
+        workingDirectory = WorkingDirectory.builder()
+            .id("workingDir")
+            .type(WorkingDirectory.class.getName())
+            .tasks(
+                List.of(Pause.builder()
+                    .id("pause")
+                    .type(Pause.class.getName())
+                    .delay(Duration.ofSeconds(1L))
+                    .build()
+                )
+            )
+            .build();
+
+        assertThat(modelValidator.isValid(workingDirectory).isPresent(), is(true));
+        assertThat(modelValidator.isValid(workingDirectory).get().getMessage(), containsString("Only runnable tasks are allowed as children of a WorkingDirectory task"));
+
+        // worker group at the subtasks level
+        workingDirectory = WorkingDirectory.builder()
+            .id("workingDir")
+            .type(WorkingDirectory.class.getName())
+            .tasks(
+                List.of(Log.builder()
+                    .id("log")
+                    .type(Log.class.getName())
+                    .message("Hello World")
+                    .workerGroup(new WorkerGroup("toto"))
+                    .build()
+                )
+            )
+            .build();
+
+        assertThat(modelValidator.isValid(workingDirectory).isPresent(), is(true));
+        assertThat(modelValidator.isValid(workingDirectory).get().getMessage(), containsString("Cannot set a Worker Group in any WorkingDirectory sub-tasks, it is only supported at the WorkingDirectory level"));
+
+    }
+}
