fix(executions): don't remove worker task result for killed execution

As killing an executuion is asynchronous, it is inherently racy.
So when we kill an execution it move to the rerminal state which then will remove any worker task result to purge eagerly the queue table.

But if such worker task result arrives late and was not already processed by the executor, it will be purged before ever been able to be processed so the task would nevert be updated as KILLED.

Note: this may un-flaky some falky unit tests

Fixes https://github.com/kestra-io/kestra-ee/issues/6040

webserver/src/test/java/io/kestra/webserver/controllers/api/ExecutionControllerRunnerTest.java

@@ -1293,7 +1293,6 @@ class ExecutionControllerRunnerTest {
         assertThat(executions.getTotal()).isEqualTo(4L);
     }
 
-    @FlakyTest
     @Test
     @LoadFlows({"flows/valids/pause-test.yaml"})
     void killExecutionPaused() throws TimeoutException, QueueException {
@@ -1311,8 +1310,7 @@ class ExecutionControllerRunnerTest {
         assertThat(killedExecution.getTaskRunList()).hasSize(1);
     }
 
-    // This test is flaky on CI as the flow may be already SUCCESS when we kill it if CI is super slow
-    @RetryingTest(5)
+    @Test
     @LoadFlows({"flows/valids/sleep-long.yml"})
     void killExecution() throws TimeoutException, InterruptedException, QueueException {
         // listen to the execution queue