[Java] Fix Potential Flaky Tests

Created by: xiedaxia1hao

This PR fixes some potential flaky tests in org.openapitools.codegen.java.AbstractJavaCodegenTest file.

In these tests, we assigned some hardcoded elements into the codegen's AdditionalModelTypeAnnotations.

However, according to the code where we set this value, we split the input string by a regex, convert it to a HashSet, and store in an ArrayList:

// org/openapitools/codegen/languages/AbstractJavaCodegen.java:347
if (additionalProperties.containsKey(ADDITIONAL_MODEL_TYPE_ANNOTATIONS)) {
    String additionalAnnotationsList = additionalProperties.get(ADDITIONAL_MODEL_TYPE_ANNOTATIONS).toString();
    this.setAdditionalModelTypeAnnotations(new ArrayList<>(Sets.newHashSet(additionalAnnotationsList.trim().split("\\s*(;|\\r?\\n)\\s*"))));
}

The problem is that HashSet is not guarantee that the order will remain constant over time according to the Java documentation. Thus, these assertions will fail in some platforms or specific machines that adopt a different iteration order.

To fix it, I sort the both additionalModelTypeAnnotations and codegen.getAdditionalModelTypeAnnotations() to make sure that their order is deterministic.

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