Find unique @⁠TestBean factory methods in class hierarchy

I accidentally introduced a regression in commit d185bb1d97 by no
longer checking the number of unique method names found when searching
for @⁠TestBean factory methods.

This commit reintroduces that check and introduces a proper unit test
in TestBeanOverrideProcessorTests.

It turns out that we already had an integration test that was intended
to check for this scenario; however, that test actually did not test
this scenario due to a copy-and-paste error. Thus, this commit also
updates TestBeanInheritanceIntegrationTests so that
fieldInSupertypeWithPrioritizedFactoryMethodInSubtype() tests what it's
supposed to.

spring-test/src/main/java/org/springframework/test/context/bean/override/convention/TestBeanOverrideProcessor.java

@@ -92,16 +92,16 @@ class TestBeanOverrideProcessor implements BeanOverrideProcessor {
 
 		Set<Method> methods = findMethods(clazz, methodFilter);
 
-		int methodCount = methods.size();
-		Assert.state(methodCount > 0, () -> """
+		Assert.state(!methods.isEmpty(), () -> """
 				Failed to find a static test bean factory method in %s with return type %s \
 				whose name matches one of the supported candidates %s""".formatted(
 						clazz.getName(), methodReturnType.getName(), supportedNames));
 
-		Assert.state(methodCount == 1, () -> """
+		long uniqueMethodNameCount = methods.stream().map(Method::getName).distinct().count();
+		Assert.state(uniqueMethodNameCount == 1, () -> """
 				Found %d competing static test bean factory methods in %s with return type %s \
 				whose name matches one of the supported candidates %s""".formatted(
-					methodCount, clazz.getName(), methodReturnType.getName(), supportedNames));
+						uniqueMethodNameCount, clazz.getName(), methodReturnType.getName(), supportedNames));
 
 		return methods.iterator().next();
 	}