flaky ParallelTestActionBuilderTest

the [`ParallelTestActionBuilderTest`](https://github.com/citrusframework/citrus/blob/c4795f79c491e0d9b0072ef4edbbae1513795780/runtime/citrus-testng/src/test/java/org/citrusframework/actions/dsl/ParallelTestActionBuilderTest.java#L32) is flaky. sometimes it failes:

```shell
Error: Tests run: 99, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 11.747 s <<< FAILURE! - in TestSuite
Error: testParallelBuilderNestedContainer(org.citrusframework.actions.dsl.ParallelTestActionBuilderTest) Time elapsed: 0.222 s <<< FAILURE!
java.lang.AssertionError: expected [class org.citrusframework.actions.EchoAction] but found [class org.citrusframework.container.Sequence]
at org.citrusframework.actions.dsl.ParallelTestActionBuilderTest.testParallelBuilderNestedContainer(ParallelTestActionBuilderTest.java:79)

[INFO]
[INFO] Results:
[INFO]
Error: Failures:
Error: ParallelTestActionBuilderTest.testParallelBuilderNestedContainer:79 expected [class org.citrusframework.actions.EchoAction] but found [class org.citrusframework.container.Sequence]
[INFO]
Error: Tests run: 99, Failures: 1, Errors: 0, Skipped: 0
```

and well, sometimes it does not. sample build of PR #959: https://github.com/citrusframework/citrus/actions/runs/5699958670/job/15450936610?pr=959.

it does so on localhost too.