Make distinct code and console admonitions so readers are less likely to miss them (#20585)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

docs/design/kernel/paged_attention.md

@@ -448,7 +448,7 @@ elements of the entire head for all context tokens. However, overall,
 all results for output have been calculated but are just stored in
 different thread register memory.
 
-??? Code
+??? code
 
     ```cpp
     float* out_smem = reinterpret_cast<float*>(shared_mem);