Properly resolve @⁠TestBean factory method within class hierarchy

Prior to this commit, the search algorithm used to locate a @⁠TestBean
factory method within a test class hierarchy incorrectly found factory
methods declared in subclasses or nested test classes "below" the class
in which the @⁠TestBean field was declared. This resulted in "duplicate
bean override" failures for @⁠TestBean overrides which are clearly not
duplicates but rather "overrides of an override".

This commit ensures that @⁠TestBean factory method resolution is
consistent in type hierarchies as well as in enclosing class
hierarchies (for @⁠Nested test classes) by beginning the search for a
factory method in the class which declares the @⁠TestBean field.

Closes gh-34204

framework-docs/modules/ROOT/pages/testing/annotations/integration-spring/annotation-testbean.adoc

@@ -92,8 +92,10 @@ Java::
 
 [TIP]
 ====
-Spring searches for the factory method to invoke in the test class, in the test class
-hierarchy, and in the enclosing class hierarchy for a `@Nested` test class.
+To locate the factory method to invoke, Spring searches in the class in which the
+`@TestBean` field is declared, in one of its superclasses, or in any implemented
+interfaces. If the `@TestBean` field is declared in a `@Nested` test class, the enclosing
+class hierarchy will also be searched.
 
 Alternatively, a factory method in an external class can be referenced via its
 fully-qualified method name following the syntax `<fully-qualified class name>#<method name>`