Test operation security serialization

[kriptoburak]

Summary

• Add a Swagger Core model serialization regression for operation security alternatives.
• Assert the serialized OpenAPI keeps the anonymous requirement before the API key requirement.

Validation

• Static whitespace check passed before commit.
• Not run: this environment does not have a Java runtime.

[ewaostrowska]

Thanks for the contribution @kriptoburak . Before we can determine whether this test should be added, could you please provide some additional context?

The PR is currently missing:

• A link to the issue, user report, or regression that motivated this change.
• A minimal example showing the observed behavior on the current master branch.
• The actual serialized output and the expected serialized output.
• Explanation on what regression or future change it is intended to protect against.
• If this is intended to fix an existing problem, the corresponding production-code change. At present, the PR only adds a test.

With that information, we can assess whether this is a useful regression test, documentation of existing behavior, or whether an implementation fix is also needed.