Fix duplicated tests

[noojung]

I found some tests that tested the same behavior.
This PR updates them to cover distinct scenarios or removes them when they are redundant.

• JdbcTemplateTests: sqlUpdateWithThreadConnection() duplicated sqlUpdate(). Bind a connection to the current thread and verify that it is reused without being closed.
• AnnotationExceptionHandlerMethodResolverTests: resolveMethodInherited() duplicated resolveMethodFromAnnotation(). Use InheritedController to verify that exception handler annotations are found on overridden methods in the superclass.
• TransactionAwareConnectionFactoryProxyTests: getTargetConnectionShouldReturnTargetConnection() duplicated unwrapShouldReturnTargetConnection(). Call ConnectionFactoryUtils.getTargetConnection() instead of unwrap().
• WebMvcStompWebSocketEndpointRegistrationTests: allowedOrigins() duplicated sameOrigin(). Configure an explicit origin in allowedOrigins() and verify the interceptor's allowed origins in both tests.
• ExceptionHandlingWebHandlerTests: thrownExceptionBecomesErrorSignal() duplicated handleErrorSignal(). Enable the flag in thrownExceptionBecomesErrorSignal() to cover the catch (Throwable) block in ExceptionHandlingWebHandler. (supersedes Fix thrown exception setup in ExceptionHandlingWebHandlerTests #37233)
• StringMessageConverterTests: remove fromMessageByteArray(), which duplicated fromByteArrayMessage().
• SubProtocolWebSocketHandlerTests: remove noSubProtocolNoDefaultHandler(), which duplicated noSubProtocolTwoHandlers().