XMLParserTest is OS language dependent

[sebtiem]

While working on another pr, I realized that one of the tests in XMLParserTest are always failing due to my non-english OS language:
During XMLParserTest.validateShouldNotBeVulnerableToXxe, exception messages are being parsed against English hardcoded exception strings.
The locale of those exception messages comes from Locale.getDefault() in a XML11Configuration constructor.
Setting the language directly in the test execution solves the issue.