Spring Security Test fails due to HttpMethod changes

Describe the bug Due to changes related to spring-projects/spring-framework#27697, the DefaultFilterInvocationSecurityMetadataSourceTests.unknownHttpMethodIsRejected test now fails. HttpMethod now supports custom methods, so UNKNOWN is no longer considered an invalid method.

To Reproduce Run DefaultFilterInvocationSecurityMetadataSourceTests.unknownHttpMethodIsRejected.

Expected behavior Tests should pass on main. To follow spring-framework, this test should be removed.