pin LMCache to v0.3.9 or greater with vLLM v0.15.0 (#33440)

Signed-off-by: greg pereira <grpereir@redhat.com>
Co-authored-by: Michael Goin <mgoin64@gmail.com>
(cherry picked from commit d6416fdd)

requirements/kv_connectors.txt

-lmcache
+lmcache >= 0.3.9
 nixl >= 0.7.1 # Required for disaggregated prefill