Since the rewrite of ConcurrentLruCache in Spring Framework 6.0, an
attempt to create a ConcurrentLruCache with zero capacity results in an
IllegalArgumentException even though the documentation states that zero
capacity indicates "no caching, always generating a new value".
This commit restores the ability to configure a ConcurrentLruCache with
zero capacity and introduces corresponding tests (which were first
verified against the 5.3.x branch to ensure backward compatibility).
See gh-26320
Closes gh-31317
06658c3c71