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
cd2fbb1ec5