Fix @transactional support on suspending function

With this commit, @transactional on suspending functions
returning a value now commits the transaction properly.

Closes gh-25998

Author: sdeleuze

spring-tx/src/main/java/org/springframework/transaction/interceptor/TransactionAspectSupport.java

@@ -875,8 +875,8 @@ public Object invokeWithinTransaction(Method method, @Nullable Class<?> targetCl
 
 			String joinpointIdentification = methodIdentification(method, targetClass, txAttr);
 
-			// Optimize for Mono
-			if (Mono.class.isAssignableFrom(method.getReturnType())) {
+			// For Mono and suspending functions not returning kotlinx.coroutines.flow.Flow
+			if (Mono.class.isAssignableFrom(method.getReturnType()) || (KotlinDetector.isSuspendingFunction(method) && !COROUTINES_FLOW_CLASS_NAME.equals(new MethodParameter(method, -1).getParameterType().getName()))) {
 				return TransactionContextManager.currentContext().flatMap(context ->
 						createTransactionIfNecessary(rtm, txAttr, joinpointIdentification).flatMap(it -> {
 							try {

spring-tx/src/test/kotlin/org/springframework/transaction/annotation/CoroutinesAnnotationTransactionInterceptorTests.kt

@@ -19,7 +19,6 @@ package org.springframework.transaction.annotation
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.runBlocking
 import org.assertj.core.api.Assertions
-import org.junit.jupiter.api.Disabled
 import org.junit.jupiter.api.Test
 import org.springframework.aop.framework.ProxyFactory
 import org.springframework.transaction.interceptor.TransactionInterceptor
@@ -64,7 +63,6 @@ class CoroutinesAnnotationTransactionInterceptorTests {
 	}
 
 	@Test
-	@Disabled("Currently fails due to gh-25998")
 	fun suspendingValueSuccess() {
 		val proxyFactory = ProxyFactory()
 		proxyFactory.setTarget(TestWithCoroutines())