Prior to this commit, AnnotationAttributes#assertNotException checked if
the attribute value was an instance of Exception. Although this was
typically sufficient, the scope was not always broad enough -- for
example, if AnnotationReadingVisitorUtils#convertClassValues stored a
Throwable in the map (such as a LinkageError).
This commit fixes this by checking for an instance of Throwable in
AnnotationAttributes#assertNotException.
Closes gh-23424
a092dc055e